[media] doc-rst: add opera-firmware.rst to DVB docs

This file is shown OK with ReST. Yet, as we changed the
place where the get_dvb_firmware script is, we need to
update it.

While here, move the author's name to the beginning of the
file.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>