[media] saa7115: initialize demod type and add the needed pads

The saa7115 driver is used on several em28xx-based devices.
Now that we're about to add MC support to em28xx, we need to
be sure that the saa711x demod will be properly mapped at MC.

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>