media: v4l: vsp1: Store pipeline pointer in vsp1_entity

Various types of objects subclassing vsp1_entity currently store a
pointer to the pipeline. Move the pointer to vsp1_entity to simplify the
code and avoid storing the pipeline in more entity subclasses later.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>