media: dt-bindings: media: rkisp1: Add port for parallel interface

The rkisp1 can take an input on the parallel interface. Add a port for
it, and update the required field. At least one port is required, and
both may be specified.

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>