drm/amd/display: remove psr state condition when psr exit case

[Why]
DMCU need to wait a vblank to handle psr enter command. When psr exit
coming before vblank, the psr exit command will be skip because current
psr state is disable.

[How]
remove psr state condition when psr exit case

Signed-off-by: Lewis Huang <Lewis.Huang@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>