V4L/DVB (7407): tuner-simple: add module options to specify rf input

Add module options to tuner-simple, called "atv_input" and "dtv_input"
to specify which rf input to use on devices with multiple rf inputs.
If the module option is not specified, then the driver will autoselect
the rf input, as per previous behavior.

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