media: vidtv: add basic support for DVBv5 stats

The current stats code is broken on so many ways. It ends
reporting 0 for signal strengh, and the work queue doesn't
run. If it would run, the code would crash.

Fix such issues and add the minimum stuff for DVBv5 stats.

Right now, only strength and cnr and UCB are implemented.
pre/post BER stats will always return zero.

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