V4L/DVB (3239): reorganize tuner-simple threshold structure.

- Create an array containing frequency threshold and control byte.
- allows for an arbitrary amount of
frequency ranges to be set, like dvb-pll.
- improves code readability.
Signed-off-by: Michael Krufky <mkrufky@m1k.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@brturbo.com.br>