media: dt-bindings: media: renesas-ceu: Add more endpoint properties

As the v4l2-fwnode framework now allows specifying defaults configurations,
expand the description of the optional endpoint properties for the CEU
interface to better explain which are their defaults values.

Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>