drm: rcar-du: Add plane allocation debugging
drm: rcar-du: Add plane allocation debugging

Plane allocation is a complex process, add debugging statements to help
finding out what could might wrong.

Signed-off-by: Laurent Pinchart <ae960578cc5eca7b9b1dbc37d9caa6cb634f35e0@ideasonboard.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs