V4L/DVB (13988): [STV090x] Configuration parameters adc1_range, adc2_range, tuner_bbgain

Add parameters adc1_range, adc2_range and tuner_bbgain to the config struct.
Defaults: adc1_range = adc2_range = 2Vpp, tuner_bbgain = 10db

Signed-off-by: Oliver Endriss <o.endriss@gmx.de>
Signed-off-by: Manu Abraham <abraham.manu@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>