drm/amdgpu: Add first_non_cp and last_non_cp in amdgpu_doorbell_index

They will be used to inform KFD the doorbell range not usable for CP.

Signed-off-by: Yong Zhao <Yong.Zhao@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>