ASoC: dt-bindings: rockchip: i2s-tdm: Document audio graph port

Document the 'port' property to allow the Rockchip I2S TDM controller to
be used in conjunction with the audio-graph-card.

The property will be used to provide an endpoint for binding to the
other side of the audio link.
Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
Link: https://lore.kernel.org/r/20230315114806.3819515-6-cristian.ciocaltea@collabora.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/rockchip,i2s-tdm.yaml

@@ -86,6 +86,10 @@ properties:
         - tx-m
         - rx-m
 
+  port:
+    $ref: audio-graph-port.yaml#
+    unevaluatedProperties: false
+
   rockchip,grf:
     $ref: /schemas/types.yaml#/definitions/phandle
     description: