ASoC: dt-bindings: uniphier: Add description of each port number

To eliminate FIXME, add descriptions of what each port number is
associated with.

Cc: Rob Herring <robh@kernel.org>
Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Link: https://lore.kernel.org/r/1633313546-23258-1-git-send-email-hayashi.kunihiko@socionext.com


Signed-off-by: Mark Brown <broonie@kernel.org>