ASoC: dt-bindings: renesas,rsnd.yaml: add common port-def

renesas,rsnd uses both "ports" has "port", and these are very similar.
To avoid duplicated definitions, this patch adds common port-def.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/87sf9eb1ln.wl-kuninori.morimoto.gx@renesas.com


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