if board uses AZ rather than ACP, we power down acp
through smu to save power.

v2: handle S3/S4 and hw_fini (Alex)
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>