[media] dvb-frontends/stv0367: selectable QAM FEC Lock status register

In some configurations (due to different PIN config, wiring or so), the
QAM FECLock might be signalled using a different register than
F367CAB_QAMFEC_LOCK (e.g. F367CAB_DESCR_SYNCSTATE on Digital Devices hw),
so make that register selectable.

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