[media] v4l: vsp1: Decouple pipeline end of frame processing from vsp1_video

To make the pipeline structure and operations usable without video
devices the frame end processing must be decoupled from struct
vsp1_video. Implement this by calling the video frame end function
indirectly through a function pointer in struct vsp1_pipeline.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>