[media] v4l: vsp1: Support VSP1 instances without any UDS

Not all VSP1 instances include a UDS. Make the renesas,#uds DT property
optional and accept a number of UDS equal to 0 as valid.

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