[media] DocBook: reformat FE_GET_INFO ioctl documentation

The DVB part of the docbook has a completely different format
than the V4L2 part, as it was written as a separate document.

As the V4L2 documentation is on better shape, and its format
allows adding more information, let's use it for FE_GET_INFO
and gradually update the non-legacy DVB ioctls using the new
format.
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>