ASoC: dt-bindings: socionext: Use audio-graph-port schema

ASoC: dt-bindings: socionext: Use audio-graph-port schema

Convert the Socionext audio schemas to use audio-graph-port.yaml schema
for 'port' nodes.

The number and numbering of port nodes should be documented, but is not.
Leave a FIXME here so others don't copy.

Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Liam Girdwood <lgirdwood@gmail.com>
Cc: Mark Brown <broonie@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210331142748.2163272-4-robh@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>