dt-bindings: usb: mtu3: add support property role-switch-default-mode

Add support optional property of role-switch-default-mode,
used to set default mode while usb role is USB_ROLE_NONE when use
usb-role-switch to switch mode.
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/1626340078-29111-4-git-send-email-chunfeng.yun@mediatek.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/usb/mediatek,mtu3.yaml

@@ -116,6 +116,10 @@ properties:
     description: Support role switch.
     type: boolean
 
+  role-switch-default-mode:
+    enum: [host, peripheral]
+    default: host
+
   connector:
     $ref: /connector/usb-connector.yaml#
     description:
@@ -184,6 +188,7 @@ patternProperties:
 dependencies:
   connector: [ 'usb-role-switch' ]
   port: [ 'usb-role-switch' ]
+  role-switch-default-mode: [ 'usb-role-switch' ]
   wakeup-source: [ 'mediatek,syscon-wakeup' ]
 
 required:
@@ -288,6 +293,7 @@ examples:
         wakeup-source;
         dr_mode = "otg";
         usb-role-switch;
+        role-switch-default-mode = "host";
         #address-cells = <1>;
         #size-cells = <1>;
         ranges;