[media] v4l: vsp1: Move frame sequence number from video node to pipeline

The frame sequence number is global to the pipeline, there's no need to
store copies in each video node.

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