V4L/DVB (6228): dvb-pll: add module option to specify rf input

Add a module option to dvb-pll, called "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>