drm/amdgpu: add ATHUB Clock Gating support for yellow carp

ATHUB MGCG/MGLS is enabled by default.
Adding ATHUB MGCG/MGLS flag to ensure athub mgcg/ls enabled.

Signed-off-by: Aaron Liu <aaron.liu@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>