[media] fimc-lite: Add ISP FIFO output support

Add second source media pad for the FIFO data output to FIMC-IS
and implement subdev s_stream op for configurations where FIMC-LITE
is used as a glue logic between FIMC-IS and MIPI-CSIS or an image
sensor. The second source media pad will be linked to the FIMC-LITE
video node.
For proper configuration the attached image sensor/video encoder
properties are needed, like video bus type, signal polarities, etc.
For this purpose there is a small routine added that walks the
pipeline and returns the sensor subdev.

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