media: dt-bindings: tvp5150: Add input port connectors DT bindings

The TVP5150/1 decoders support different video input sources to their
AIP1A/B pins.

Possible configurations are as follows:
  - Analog Composite signal connected to AIP1A.
  - Analog Composite signal connected to AIP1B.
  - Analog S-Video Y (luminance) and C (chrominance)
    signals connected to AIP1A and AIP1B respectively.

This patch extends the device tree bindings documentation to describe
how the input connectors for these devices should be defined in a DT.

Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>