We use the same check already in the atomic core, so might as well
make this official. And it's also reused in e.g. i915.
Motivated by Maarten's idea to extract a connector_changed state out
of mode_changed.
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-By: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
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