dt-bindings: i2c: update bindings for mt8188 soc

Add a DT binding documentation for the mt8188 soc.
Signed-off-by: Kewei Xu <kewei.xu@mediatek.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Qii Wang <qii.wang@mediatek.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>

Documentation/devicetree/bindings/i2c/i2c-mt65xx.yaml

@@ -27,6 +27,7 @@ properties:
       - const: mediatek,mt8173-i2c
       - const: mediatek,mt8183-i2c
       - const: mediatek,mt8186-i2c
+      - const: mediatek,mt8188-i2c
       - const: mediatek,mt8192-i2c
       - items:
           - enum: