[media] v4l: vsp1: Allocate pipelines on demand

Instead of embedding pipelines in the vsp1_video objects allocate them
on demand when they are needed. This fixes the streamon race condition
where pipelines objects from different video nodes could be used for the
same pipeline.

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