dt-bindings: mediatek: add support for mt6779 reference board

Update binding document for mt6779 reference board
Signed-off-by: Mars Cheng <mars.cheng@mediatek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>

Documentation/devicetree/bindings/arm/mediatek.yaml

@@ -46,6 +46,10 @@ properties:
           - enum:
               - mediatek,mt6765-evb
           - const: mediatek,mt6765
+      - items:
+          - enum:
+              - mediatek,mt6779-evb
+          - const: mediatek,mt6779
       - items:
           - enum:
               - mediatek,mt6795-evb