ASoC: dt-bindings: mt8183: add a property "mediatek, hdmi-codec"

Adds an optional property "mediatek,hdmi-codec".
Signed-off-by: Tzung-Bi Shih <tzungbi@google.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200710052505.3664118-2-tzungbi@google.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/mt8183-mt6358-ts3a227-max98357.txt

@@ -9,6 +9,7 @@ Optional properties:
 - mediatek,headset-codec: the phandles of ts3a227 codecs
 - mediatek,ec-codec: the phandle of EC codecs.
                      See google,cros-ec-codec.txt for more details.
+- mediatek,hdmi-codec: the phandles of HDMI codec
 
 Example:
 
@@ -16,6 +17,7 @@ Example:
 		compatible = "mediatek,mt8183_mt6358_ts3a227_max98357";
 		mediatek,headset-codec = <&ts3a227>;
 		mediatek,ec-codec = <&ec_codec>;
+		mediatek,hdmi-codec = <&it6505dptx>;
 		mediatek,platform = <&afe>;
 	};