ASoC: dt-bindings: ak4613: enable Of-graph (Audio-Graph-Card) style

ASoC: dt-bindings: ak4613: enable Of-graph (Audio-Graph-Card) style

ak4613 is possible to use Of-graph (Audio-Graph-Card) style,
but we need to indicate it. Otherwise we will get below warning.
This patch add it.

${LINUX}/arch/arm64/boot/dts/renesas/r8a77950-salvator-x.dtb: codec@10: 'port' does not match any of the regexes: '^asahi-kasei,in[1-2]-single-end$', '^asahi-kasei,out[1-6]-single-end$', 'pinctrl-[0-9]+'
	From schema: ${LINUX}/Documentation/devicetree/bindings/sound/ak4613.yaml

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/87ilgx7rfp.wl-kuninori.morimoto.gx@renesas.com
Signed-off-by: Mark Brown <broonie@kernel.org>