media: tvp5150: add input source selection of_graph support

This patch adds the of_graph support to describe the tvp input connections.
Physical the TVP5150 has three ports: AIP1A, AIP1B and YOUT. As result
of discussion [1],[2] the device-tree maps these ports 1:1. Look at the
Documentation for more information. Since the TVP5150 is a converter/bridge
the device-tree must contain at least 1-input and 1-output port. The
mc-connectors and mc-links are only created if the device-tree contains the
corresponding connector nodes. If more than one connector is available the
media_entity_operations.link_setup() callback ensures that only one
connector is active.

[1] https://www.spinics.net/lists/linux-media/msg138545.html
[2] https://www.spinics.net/lists/linux-media/msg138546.htmlSigned-off-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>