media: dvb-frontends/stv0367: initial DDB DVBv5 stats, implement ucblocks

This adds the basics to stv0367ddb_read_status() to be able to properly
provide signal statistics in DVBv5 format. Also adds UCB readout and
provides those values. Also, don't return -EINVAL in ddb_read_status()
if active_demod_state indicates no delivery system.

Signed-off-by: Daniel Scheller <d.scheller@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>