drm/amd/display: Bail from dm_check_crtc_cursor if no relevant change

If no plane was newly enabled or changed scaling, there can be no new
scaling mismatch with the cursor plane.

By not pulling non-cursor plane states into all atomic commits while
the cursor plane is enabled, this avoids synchronizing all cursor plane
changes to vertical blank, which caused the following IGT tests to fail:

kms_cursor_legacy@cursor-vs-flip.*
kms_cursor_legacy@flip-vs-cursor.*

Fixes: 003048dd ("drm/amd/display: Check all enabled planes in dm_check_crtc_cursor")
Signed-off-by: Michel Dänzer <mdaenzer@redhat.com>
Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>