dt-bindings: display: mediatek: add vdosys1 MERGE property for mt8195

MT8195 vdosys1 merge1 to merge4 have HW mute function.
Add MERGE additional mute property description.
Signed-off-by: Nancy.Lin <nancy.lin@mediatek.com>
Acked-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>

Documentation/devicetree/bindings/display/mediatek/mediatek,merge.yaml

@@ -61,6 +61,10 @@ properties:
       command to SMI to speed up the data rate.
     type: boolean
 
+  mediatek,merge-mute:
+    description: Support mute function. Mute the content of merge output.
+    type: boolean
+
   mediatek,gce-client-reg:
     description: The register of client driver can be configured by gce with
       4 arguments defined in this property, such as phandle of gce, subsys id,