I just installed the new kernel 4.4.1-gentoo and there in menuconfig I found "Enable amdgpu support for CIK parts" option.
[ 38.871] (II) LoadModule: "glx"
[ 38.954] (II) Loading /usr/lib64/xorg/modules/extensions/libglx.so
[ 39.200] (II) Module glx: vendor="X.Org Foundation"
[ 39.200] compiled for 1.17.4, module version = 1.0.0
[ 39.200] ABI class: X.Org Server Extension, version 9.0
[ 39.200] (==) AIGLX enabled
[ 39.200] (II) Applying OutputClass "AMDgpu" to /dev/dri/card0
[ 39.200] loading driver: amdgpu
[ 39.200] (==) Matched amdgpu as autoconfigured driver 0
[ 39.200] (==) Matched ati as autoconfigured driver 1
[ 39.200] (==) Matched ati as autoconfigured driver 2
[ 39.200] (==) Matched modesetting as autoconfigured driver 3
[ 39.200] (==) Matched fbdev as autoconfigured driver 4
[ 39.200] (==) Matched vesa as autoconfigured driver 5
[ 39.200] (==) Assigned the driver to the xf86ConfigLayout
[ 39.200] (II) LoadModule: "amdgpu"
[ 39.200] (II) Loading /usr/lib64/xorg/modules/drivers/amdgpu_drv.so
[ 39.271] (II) Module amdgpu: vendor="X.Org Foundation"
[ 39.271] compiled for 1.17.4, module version = 0.0.1
[ 39.271] Module class: X.Org Video Driver
[ 39.271] ABI class: X.Org Video Driver, version 19.0
[ 39.271] (II) LoadModule: "ati"
[ 39.271] (II) Loading /usr/lib64/xorg/modules/drivers/ati_drv.so
[ 39.305] (II) Module ati: vendor="X.Org Foundation"
[ 39.305] compiled for 1.17.4, module version = 7.5.0
[ 39.305] Module class: X.Org Video Driver
[ 39.305] ABI class: X.Org Video Driver, version 19.0
[ 39.305] (II) LoadModule: "radeon"
[ 39.305] (II) Loading /usr/lib64/xorg/modules/drivers/radeon_drv.so
[ 39.336] (II) Module radeon: vendor="X.Org Foundation"
[ 39.336] compiled for 1.17.4, module version = 7.5.0
[ 39.336] Module class: X.Org Video Driver
[ 39.336] ABI class: X.Org Video Driver, version 19.0
[ 39.336] (II) LoadModule: "modesetting"
[ 39.336] (II) Loading /usr/lib64/xorg/modules/drivers/modesetting_drv.so
[ 39.365] (II) Module modesetting: vendor="X.Org Foundation"
[ 39.365] compiled for 1.17.4, module version = 1.17.4
[ 39.365] Module class: X.Org Video Driver
[ 39.365] ABI class: X.Org Video Driver, version 19.0
[ 39.365] (II) LoadModule: "fbdev"
[ 39.379] (WW) Warning, couldn't open module fbdev
[ 39.379] (II) UnloadModule: "fbdev"
[ 39.379] (II) Unloading fbdev
[ 39.379] (EE) Failed to load module "fbdev" (module does not exist, 0)
[ 39.379] (II) LoadModule: "vesa"
[ 39.379] (WW) Warning, couldn't open module vesa
[ 39.379] (II) UnloadModule: "vesa"
[ 39.379] (II) Unloading vesa
[ 39.379] (EE) Failed to load module "vesa" (module does not exist, 0)
[ 39.379] (II) AMDGPU: Driver for AMD Radeon chipsets: BONAIRE, BONAIRE, BONAIRE,
BONAIRE, BONAIRE, BONAIRE, BONAIRE, BONAIRE, BONAIRE, KABINI, KABINI,
KABINI, KABINI, KABINI, KABINI, KABINI, KABINI, KABINI, KABINI,
KABINI, KABINI, KABINI, KABINI, KABINI, KABINI, KAVERI, KAVERI,
KAVERI, KAVERI, KAVERI, KAVERI, KAVERI, KAVERI, KAVERI, KAVERI,
KAVERI, KAVERI, KAVERI, KAVERI, KAVERI, KAVERI, KAVERI, KAVERI,
KAVERI, KAVERI, KAVERI, HAWAII, HAWAII, HAWAII, HAWAII, HAWAII,
HAWAII, HAWAII, HAWAII, HAWAII, HAWAII, HAWAII, HAWAII, TOPAZ, TOPAZ,
TOPAZ, TOPAZ, TOPAZ, TONGA, TONGA, TONGA, TONGA, TONGA, TONGA, TONGA,
TONGA, TONGA, CARRIZO, CARRIZO, CARRIZO, CARRIZO, CARRIZO, FIJI
[ 39.379] (II) RADEON: Driver for ATI Radeon chipsets:
...
[ 39.385] (II) modesetting: Driver for Modesetting Kernel Drivers: kms
[ 39.385] (++) using VT number 1
[ 39.385] (--) controlling tty is VT number 1, auto-enabling KeepTty
[ 39.385] (II) systemd-logind: releasing fd for 226:0
[ 39.400] (II) [KMS] Kernel modesetting enabled.
[ 39.400] (WW) Falling back to old probe method for modesetting
[ 39.400] (II) AMDGPU(0): Creating default Display subsection in Screen section
"Default Screen Section" for depth/fbbpp 24/32
[ 39.400] (==) AMDGPU(0): Depth 24, (--) framebuffer bpp 32
[ 39.400] (II) AMDGPU(0): Pixel depth = 24 bits stored in 4 bytes (32 bpp pixmaps)
[ 39.400] (==) AMDGPU(0): Default visual is TrueColor
[ 39.400] (==) AMDGPU(0): RGB weight 888
[ 39.400] (II) AMDGPU(0): Using 8 bits per RGB (8 bit DAC)
[ 39.400] (--) AMDGPU(0): Chipset: "BONAIRE" (ChipID = 0x665f)
[ 39.400] (II) Loading sub module "dri2"
[ 39.400] (II) LoadModule: "dri2"
[ 39.401] (II) Module "dri2" already built-in
[ 40.099] (II) Loading sub module "glamoregl"
[ 40.099] (II) LoadModule: "glamoregl"
[ 40.099] (II) Loading /usr/lib64/xorg/modules/libglamoregl.so
[ 40.147] (II) Module glamoregl: vendor="X.Org Foundation"
[ 40.148] compiled for 1.17.4, module version = 1.0.0
[ 40.148] ABI class: X.Org ANSI C Emulation, version 0.4
[ 40.148] (II) glamor: OpenGL accelerated X.org driver based.
[ 40.171] (II) glamor: EGL version 1.4 (DRI2):
[ 40.271] (II) AMDGPU(0): glamor detected, initialising EGL layer.
[ 40.271] (II) AMDGPU(0): KMS Pageflipping: enabled
[ 40.274] (II) AMDGPU(0): Output DisplayPort-0 has no monitor section
[ 40.275] (II) AMDGPU(0): Output HDMI-A-0 has no monitor section
[ 40.282] (II) AMDGPU(0): Output DVI-I-0 has no monitor section
[ 40.316] (II) AMDGPU(0): Output DVI-D-0 has no monitor section
[ 40.319] (II) AMDGPU(0): EDID for output DisplayPort-0
[ 40.320] (II) AMDGPU(0): EDID for output HDMI-A-0
[ 40.327] (II) AMDGPU(0): EDID for output DVI-I-0
[ 40.361] (II) AMDGPU(0): EDID for output DVI-D-0
[ 40.361] (II) AMDGPU(0): Manufacturer: GSM Model: 567e Serial#: 221144
[ 40.361] (II) AMDGPU(0): Year: 2008 Week: 6
[ 40.361] (II) AMDGPU(0): EDID Version: 1.3
[ 40.361] (II) AMDGPU(0): Digital Display Input
[ 40.361] (II) AMDGPU(0): Max Image Size [cm]: horiz.: 49 vert.: 32
[ 40.361] (II) AMDGPU(0): Gamma: 2.20
[ 40.361] (II) AMDGPU(0): DPMS capabilities: StandBy Suspend Off
[ 40.361] (II) AMDGPU(0): Supported color encodings: RGB 4:4:4 YCrCb 4:4:4
[ 40.361] (II) AMDGPU(0): First detailed timing is preferred mode
[ 40.361] (II) AMDGPU(0): redX: 0.635 redY: 0.342 greenX: 0.292 greenY: 0.611
[ 40.361] (II) AMDGPU(0): blueX: 0.147 blueY: 0.070 whiteX: 0.313 whiteY: 0.329
[ 40.361] (II) AMDGPU(0): Supported established timings:
...
[ 40.362] (II) AMDGPU(0): Output DisplayPort-0 disconnected
[ 40.362] (II) AMDGPU(0): Output HDMI-A-0 disconnected
[ 40.362] (II) AMDGPU(0): Output DVI-I-0 disconnected
[ 40.362] (II) AMDGPU(0): Output DVI-D-0 connected
[ 40.362] (II) AMDGPU(0): Using exact sizes for initial modes
[ 40.362] (II) AMDGPU(0): Output DVI-D-0 using initial mode 1680x1050
[ 40.362] (II) AMDGPU(0): Using default gamma of (1.0, 1.0, 1.0) unless otherwise stated.
[ 40.362] (II) AMDGPU(0): mem size init: gart size :7f563000 vram size: s:80000000 visible:f1e2000
[ 40.362] (==) AMDGPU(0): DPI set to (96, 96)
[ 40.362] (II) Loading sub module "fb"
[ 40.362] (II) LoadModule: "fb"
[ 40.362] (II) Loading /usr/lib64/xorg/modules/libfb.so
[ 40.373] (II) Module fb: vendor="X.Org Foundation"
[ 40.373] compiled for 1.17.4, module version = 1.0.0
[ 40.373] ABI class: X.Org ANSI C Emulation, version 0.4
[ 40.373] (II) Loading sub module "ramdac"
[ 40.373] (II) LoadModule: "ramdac"
[ 40.373] (II) Module "ramdac" already built-in
[ 40.373] (II) UnloadModule: "radeon"
[ 40.373] (II) Unloading radeon
[ 40.373] (II) UnloadModule: "modesetting"
[ 40.373] (II) Unloading modesetting
[ 40.373] (--) Depth 24 pixmap format is 32 bpp
[ 40.385] (II) AMDGPU(0): [DRI2] Setup complete
[ 40.385] (II) AMDGPU(0): [DRI2] DRI driver: radeonsi
[ 40.385] (II) AMDGPU(0): [DRI2] VDPAU driver: radeonsi
[ 40.385] (II) AMDGPU(0): Front buffer pitch: 6912 bytes
[ 40.386] (==) AMDGPU(0): DRI3 disabled
[ 40.386] (==) AMDGPU(0): Backing store enabled
[ 40.386] (II) AMDGPU(0): Direct rendering enabled
[ 40.513] (II) AMDGPU(0): Use GLAMOR acceleration.
[ 40.513] (II) AMDGPU(0): Acceleration enabled
[ 40.513] (==) AMDGPU(0): DPMS enabled
[ 40.513] (==) AMDGPU(0): Silken mouse enabled
[ 40.513] (II) AMDGPU(0): Set up textured video (glamor)
[ 40.514] (II) AMDGPU(0): RandR 1.2 enabled, ignore the following RandR disabled message.
[ 40.548] (--) RandR disabled
[ 40.550] (II) AIGLX: enabled GLX_MESA_copy_sub_buffer
[ 40.550] (II) AIGLX: enabled GLX_ARB_create_context
[ 40.550] (II) AIGLX: enabled GLX_ARB_create_context_profile
[ 40.550] (II) AIGLX: enabled GLX_EXT_create_context_es2_profile
[ 40.550] (II) AIGLX: enabled GLX_INTEL_swap_event
[ 40.550] (II) AIGLX: enabled GLX_SGI_swap_control and GLX_MESA_swap_control
[ 40.550] (II) AIGLX: enabled GLX_EXT_framebuffer_sRGB
[ 40.550] (II) AIGLX: enabled GLX_ARB_fbconfig_float
[ 40.550] (II) AIGLX: GLX_EXT_texture_from_pixmap backed by buffer objects
[ 40.550] (II) AIGLX: enabled GLX_ARB_create_context_robustness
[ 40.552] (II) AIGLX: Loaded and initialized radeonsi
[ 40.552] (II) GLX: Initialized DRI2 GL provider for screen 0
[ 40.962] (II) AMDGPU(0): Setting screen physical size to 444 x 277
...
[ 60.008] (II) AMDGPU(0): EDID vendor "GSM", prod id 22142
[ 60.008] (II) AMDGPU(0): Using EDID range info for horizontal sync
[ 60.008] (II) AMDGPU(0): Using EDID range info for vertical refresh
[ 60.008] (II) AMDGPU(0): Printing DDC gathered Modelines:
[ 60.008] (II) AMDGPU(0): Modeline "1680x1050"x0.0 119.00 1680 1728 1760 1840 1050 1053 1059 1080 +hsync
-vsync (64.7 kHz eP)
etc.