dt-bindings: soc: mediatek: add gce-client-reg for MUTEX

In order to allow modules with latency requirements such as MDP3
to set registers through CMDQ, add the relevant GCE property.
Signed-off-by: Moudy Ho <moudy.ho@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220610063424.7800-5-moudy.ho@mediatek.comSigned-off-by: Matthias Brugger <matthias.bgg@gmail.com>

Documentation/devicetree/bindings/soc/mediatek/mediatek,mutex.yaml

@@ -55,6 +55,18 @@ properties:
       include/dt-bindings/gce/<chip>-gce.h of each chips.
     $ref: /schemas/types.yaml#/definitions/uint32-array
 
+  mediatek,gce-client-reg:
+    $ref: /schemas/types.yaml#/definitions/phandle-array
+    items:
+      items:
+        - description: phandle of GCE
+        - description: GCE subsys id
+        - description: register offset
+        - description: register size
+    description: The register of client driver can be configured by gce with
+      4 arguments defined in this property. Each GCE subsys id is mapping to
+      a client defined in the header include/dt-bindings/gce/<chip>-gce.h.
+
 required:
   - compatible
   - reg