Currently we process page flip events on every display interrupt,
however this does not take into consideration the processing time needed
by the VSP1 utilised in the pipeline.

Register a callback with the VSP driver to obtain completion events, and
track them so that we only perform page flips when the full display
pipeline has completed for the frame.
Signed-off-by: NKieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Reviewed-by: NLaurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: NLaurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>