[media] DocBook: document V4L2_CTRL_TYPE_BITMASK

[mchehab@redhat.com: Fix a merge conflict and make compat.xml coherent with v4l2.xml]
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Sakari Ailus <sakari.ailus@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>