The chips supported by the si2157 driver have two IF outputs (either
pins 12+13 or pins 9+11). Instead of hardcoding the output to be used
add an option to choose which output shall be used.

As this patch changes the default behaviour, the IF interface is
specified in each driver currently using si2157 driver. This is to
keep bisectability.
Signed-off-by: Olli Salonen <olli.salonen@iki.fi>
Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>