V4L/DVB (7123): tuner-simple: create separate t_params and ranges lookup functions

Move some reuseable code out of simple_set_tv_freq into separate functions.

Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>