media: v4l: vsp1: Integrate DISCOM in display pipeline

The DISCOM is used to compute CRCs on display frames. Integrate it in
the display pipeline at the output of the blending unit to process
output frames.

Computing CRCs on input frames is possible by positioning the DISCOM at
a different point in the pipeline. This use case isn't supported at the
moment and could be implemented by extending the API between the VSP1
and DU drivers if needed.

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