kmssink: Remove unused planes from the selected crtc

Some hardware such as Amlogic SOCs use distinct video planes and application planes.
If this is the case, an application plane could be left active and in the way of the
video plane selected by kmssink. Any planes not used by kmssink can and should be
disconnected from the crtc.
32 jobs for !2374 with kmssink-clear-unused-planes in 56 seconds (queued for 6 seconds)
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