dt-bindings: mailbox: mtk,adsp-mbox: Add compatible for MT8188

Add compatible string for ADSP mailbox on MT8188 SoC, which is
compatible with the one used on MT8186.
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Fei Shao <fshao@chromium.org>
Signed-off-by: Jassi Brar <jassisinghbrar@gmail.com>

Documentation/devicetree/bindings/mailbox/mtk,adsp-mbox.yaml

@@ -17,9 +17,15 @@ description: |
 
 properties:
   compatible:
-    enum:
-      - mediatek,mt8195-adsp-mbox
-      - mediatek,mt8186-adsp-mbox
+    oneOf:
+      - enum:
+          - mediatek,mt8186-adsp-mbox
+          - mediatek,mt8195-adsp-mbox
+      - items:
+          - enum:
+              - mediatek,mt8188-adsp-mbox
+          - const: mediatek,mt8186-adsp-mbox
+
 
   "#mbox-cells":
     const: 0