libcamera guarantees that requests complete in sequence. This requirement is currently pushed down to pipeline handlers. Three out of four of our pipeline handlers implement that requirement based on the sole assumption that buffers will always complete in sequeuence, while the IPU3 pipeline handler implements a more complex logic. It turns out that the logic can be moved to the base PipelineHandler class with support from the Request class. Do so to simplify the pipeline handlers. Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>