ASoC: dt-bindings: audio-graph-port: Document new DAI link flags playback-only/capture-only

Document new playback-only and capture-only flags which can be used
when dai link can only support just one direction: playback or capture
but not both.
Signed-off-by: Daniel Baluta <daniel.baluta@nxp.com>
Link: https://msgid.link/r/20231128081119.106360-3-daniel.baluta@oss.nxp.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/audio-graph-port.yaml

@@ -19,6 +19,12 @@ definitions:
     properties:
       mclk-fs:
         $ref: simple-card.yaml#/definitions/mclk-fs
+      playback-only:
+        description: port connection used only for playback
+        $ref: /schemas/types.yaml#/definitions/flag
+      capture-only:
+        description: port connection used only for capture
+        $ref: /schemas/types.yaml#/definitions/flag
 
   endpoint-base:
     allOf: