media: dt: bindings: media: Document practices for DT bindings, ports, endpoints

Port and endpoint numbering has been omitted in DT binding documentation
for a large number of devices. Also common properties the device uses have
been missed in binding documentation. Make it explicit that these things
need to be documented.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>