drm/amd/powerplay: implement set_mmhub_powergating_by_smu for Raven

mmhub PG is enabled by SMU FW only for Raven.

Signed-off-by: Eric Huang <JinHuiEric.Huang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>