ASoC: dt-bindings: imx-card: Add playback-only and capture-only property

Refer to audio graph card, add playback-only and capture-only property
for imx-audio-card.yaml for the case that only playback or capture is
supported.

Signed-off-by: Shengjiu Wang <[e-mail]>
Reviewed-by: Daniel Baluta <[e-mail]>
Reviewed-by: Iuliana Prodan <[e-mail]>
Acked-by: Rob Herring (Arm) <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

Documentation/devicetree/bindings/sound/imx-audio-card.yaml

···
         description: see tdm-slot.txt.
         $ref: /schemas/types.yaml#/definitions/uint32
 
+      playback-only:
+        description: link is used only for playback
+        $ref: /schemas/types.yaml#/definitions/flag
+
+      capture-only:
+        description: link is used only for capture
+        $ref: /schemas/types.yaml#/definitions/flag
+
       cpu:
         description: Holds subnode which indicates cpu dai.
         type: object
···
     required:
       - link-name
       - cpu
+
+    allOf:
+      - not:
+          required:
+            - playback-only
+            - capture-only
 
     additionalProperties: false