[Why]
PSR needs to be enabled on DCN30. This is the driver part of PSR
enablement.

Also disabled retired DMCU on driver side, since DMCU is
not supported on DCN30 anymore.

[How]
Add necessary changes to enable PSR on DCN30.
Signed-off-by: Zhan Liu <zhan.liu@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>