Right now, only kAPI documentation describes the device naming.
However, such description is needed at the uAPI too. Add it,
and describe how to get an unique identifier for a given device.
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>