V4L/DVB (7129): tuner-simple: move device-specific code into three separate functions

Move the switch..case blocks with device-specific code from functions
simple_set_tv_freq and simple_set_radio_freq

...into three new functions:
simple_std_setup, simple_post_tune and simple_radio_bandswitch
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>