[media] v4l/dvb: add support for AVerMedia AVerTV Red HD+ (A850T)

The AVerTV Red HD+ (A850T) is basically the same as the existing
AVerTV Volar Black HD (A850), but is specific to the french market.
The A850T identifies itself as a A850, but has its own PID. It even
suffers from the same EEPROM deficiencies.

This is based off a collection of information gathered from the
french support forums for Ubuntu, which I tried to properly format
into this patch:
  http://forum.ubuntu-fr.org/viewtopic.php?pid=3322825



Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>