kernel: Fix kmod-drm-amdgpu and kmod-drm-radeon dependencies

kernel: Fix kmod-drm-amdgpu and kmod-drm-radeon dependencies

Currently the Geode builds fails on following kernel module missing
dependencies:

 Package kmod-drm-amdgpu is missing dependencies for the following libraries:
 backlight.ko
 drm_kms_helper.ko
 fb.ko
 ttm.ko

So this patch tries to fix the kmod-drm-amdgpu module dependecies.

Fixes: 2f239c0 ("x86: video: add amdgpu DRM kernel package")
Fixes: 2f6918e ("x86: video: add radeon DRM module support")
Tested-by: Tomasz Maciej Nowak <tomek_n@o2.pl>
Signed-off-by: Lucian Cristian <lucian.cristian@gmail.com>