[Why]
It's currently tied to Z10 support, and is required for Z10, but
we can still support Z10 display off without PSR.

We currently need to skip the PSR CRTC disable to prevent stuttering
and underflow from occuring during PSR-SU.

[How]
Add a debug option to allow specifying this separately.
Reviewed-by: Robin Chen <robin.chen@amd.com>
Acked-by: Stylon Wang <stylon.wang@amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>