drm/amdgpu: Add module param to control CIK support

If AMDGPU supports CIK, add a module parameter to control CIK
support. It's on by default in AMDGPU, while it is off by default
in radeon.

Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Acked-by: Michel Dänzer <michel.daenzer@amd.com>