[media] v4l-dv-timings.h: Add to device-drivers DocBook

There are already markups for documentation at v4l-dv-timings.h,
however, they're not properly formatted.

Convert them to the right format and add this file to
the device-drivers DocBook.

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Acked-by: Jonathan Corbet <corbet@lwn.net>