drm/amd/display: Add IPS checks before dcn register access

[Why]
With IPS enabled a system hangs once PSR is active.
PSR active triggers transition to IPS2 state.
While in IPS2 an access to dcn registers results in hard hang.
Existing check doesn't cover for PSR sequence.

[How]
Safeguard register access by disabling idle optimization in atomic commit
and crtc scanout. It will be re-enabled on next vblank.

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Acked-by: Roman Li <roman.li@amd.com>
Signed-off-by: Roman Li <roman.li@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>