media: av7110: move driver to staging

This driver is really old, from devices that aren't
manufactured anymore for more than a decade.

Also, the decoder supports only MPEG2, with is not compatible
with several modern DVB streams.

It is also the only upstream driver relying on the DVB
"full-featured" API.

Some changes at the frontend drivers seem to have broken it
without anybody noticing.

Due to that, it sounds it is time to retire the driver for good.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>