dt-bindings: display: bridge: it66121: Add audio support

Update the ITE bridge HDMI it66121 bindings in order to
support audio.
Signed-off-by: NNicolas Belin <nbelin@baylibre.com>
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NNeil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220316135733.173950-2-nbelin@baylibre.com

Documentation/devicetree/bindings/display/bridge/ite,it66121.yaml

@@ -38,6 +38,9 @@ properties:
   interrupts:
     maxItems: 1
 
+  "#sound-dai-cells":
+    const: 0
+
   ports:
     $ref: /schemas/graph.yaml#/properties/ports