media: v4l: fwnode: v4l2_async_notifier_parse_fwnode_endpoints is deprecated

Document that v4l2_async_notifier_parse_fwnode_endpoints() is deprecated.
Its functionality has been replaced by other, better functions. Also add a
reference to an example if someone ends up wandering here.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>