drm: Move radeon and amdgpu Kconfig options into their directories

Most Kconfig options to enable a driver are in the Kconfig file
inside the relevant directory, move these two to the same.

Signed-off-by: Andrew Davis <afd@ti.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>