media: v4l: vsp1: Move DRM atomic commit pipeline setup to separate function

The DRM pipeline setup code used at atomic commit time is similar to the
setup code used when enabling the pipeline. Move it to a separate
function in order to share it.

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>