[media] v4l: vsp1: Move entity route setup function to vsp1_entity.c

The function will be used by the DU code, move it out of vsp1_video.c.

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