drm/amd/display: Workaround register access in idle race with cursor

drm/amd/display: Workaround register access in idle race with cursor

[Why]
Cursor update can be pre-empted by a request for setting target flip
submission.

This causes an issue where we're in the middle of the exit sequence
trying to log to DM, but the pre-emption starts another DMCUB
command submission that requires being out of idle.

The DC lock aqusition can fail, and depending on the DM/OS interface
it's possible that the function inserted into this thread must not fail.

This means that lock aqusition must be skipped and exit *must* occur.

[How]
Modify when we consider idle as active. Consider it exited only once
the exit has fully finished.

Consider it as entered prior to actual notification.

Since we're on the same core/thread the cached values are coherent
and we'll see that we still need to exit. Once the cursor update resumes
it'll continue doing the double exit but this won't cause a functional
issue, just a (potential) redundant operation.

Reviewed-by: Duncan Ma <duncan.ma@amd.com>
Acked-by: Wayne Lin <wayne.lin@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>