[media] v4l: vsp1: Store the display list manager in the WPF

Each WPF can process display lists independently, move the manager to
the WPF to reflect that and prepare for display list support for non-DRM
pipelines.

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