media: v4l: fwnode: Move KernelDoc documentation to the header

In V4L2 the practice is to have the KernelDoc documentation in the header
and not in .c source code files. This consequently makes the V4L2 fwnode
function documentation part of the Media documentation build.

Also correct the link related function and argument naming in
documentation and add an asterisk to v4l2_fwnode_endpoint_free()
documentation to make it proper KernelDoc documentation.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>