drm/amdgpu: enable MGCG and LS for MMHUB 3.0

Enable MMHUB 3.0 MGCG and LS features.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>