drm/amdgpu: Enable Multi Media Hub (MMHUB) Clock Gating for sienna_cichlid.

Enable mmhub clockgating.
Signed-off-by: Likun Gao <Likun.Gao@amd.com>
Reviewed-by: Kenneth Feng <kenneth.feng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/nv.c

@@ -717,6 +717,7 @@ static int nv_common_early_init(void *handle)
 		adev->cg_flags = AMD_CG_SUPPORT_GFX_MGCG |
 			AMD_CG_SUPPORT_GFX_CGCG |
 			AMD_CG_SUPPORT_GFX_3D_CGCG |
+			AMD_CG_SUPPORT_MC_MGCG |
 			AMD_CG_SUPPORT_VCN_MGCG |
 			AMD_CG_SUPPORT_JPEG_MGCG |
 			AMD_CG_SUPPORT_HDP_MGCG |