[media] s5p-fimc: Add support for sensors with multiple pads

Some sensors can have more than one pad (case of S5C73M3).
In such cases FIMC assumes the last pad of the sensor is
the source pad.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>