The WPF needs access to the current display list to configure writeback.
Add a display list pointer to the VSP1 entity .configure_stream()
operation.

Only display pipelines can make use of the display list there as
mem-to-mem pipelines don't have access to a display list at stream
configuration time. This is not an issue as writeback is only used for
display pipelines.
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>