[media] DocBook media: drop 'experimental' annotations

Drop the 'experimental' annotations. The only remaining part of the API
that is still marked 'experimental' are the debug ioctls/structs, and
that is intentional. Only the v4l2-dbg application should use those.

All others have been around for years, so it is time to drop the
'experimental' designation.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>