drm/amd/powerplay: enable ULCK DS for sienna_cichlid

Enable uclk deep sleep for sienna_cichlid.
Df cstate kicks in first, then df triggers uclk ds with the sideband.

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>