drm/amd/display: Implement PSR wait for enable/disable

[Why]
For DMUB implementation of PSR, the 'wait' parameter,
used to determine if driver should wait for PSR enable/disable,
is not implemented correctly.

[How]
Implement wait for PSR enable/disable.

Signed-off-by: Wyatt Wood <wyatt.wood@amd.com>
Reviewed-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>