[media] tvp5150: document input connectors DT bindings

The tvp5150 decoder has different input connectors so extend the device
tree binding to allow device tree source files to define the connectors
that are available on a given board.

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