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

Documentation/devicetree/bindings/sound/ak4613.yaml

@@ -25,6 +25,13 @@ properties:
   "#sound-dai-cells":
     const: 0
 
+  ports:
+    $ref: audio-graph-port.yaml#/definitions/ports
+
+  port:
+    $ref: audio-graph-port.yaml#
+    unevaluatedProperties: false
+
 patternProperties:
   "^asahi-kasei,in[1-2]-single-end$":
     description: Input Pin 1 - 2.