[media] DocBook: Add documentation for ATSC M/H properties

Those data were retrieved by looking at A/153: ATSC Mobile DTV
Standard and guessing what makes more sense to each field.

Cc: Michael Ira Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>