drm/amd/display: Enable PSR by default on newer DCN

drm/amd/display: Enable PSR by default on newer DCN

[Why]
For optimal power savings on panels that can support it.

This was previously left disabled by default because of issues with
compositors that do not pageflip and scan out directly to the
frontbuffer.

For these compositors we now have detection methods that wait for x
number of pageflips after a full update - triggered by a buffer or
format change typically.

This may introduce bugs or new cases not tested by users so this is
only currently targeting newer DCN.

[How]
Add code in DM to set PSR state by default for newer DCN while falling
back to the feature mask for older.

Add a global debug flag that can be set to disable it for either.

Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>