drm/amd/powerplay: enable SOC Clock Deep Sleep for sienna_cichlid

Enable System On Chip Clock Deep Sleep for sienna_cichlid.

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>