dt-bindings: usb: mtu3: add properties about USB Role Switch

Now the USB Role Switch is supported, so add properties about it,
and modify some description related.
Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1567070558-29417-5-git-send-email-chunfeng.yun@mediatek.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

@@ -28,8 +28,13 @@ Optional properties:
 	parent's address space
  - extcon : external connector for vbus and idpin changes detection, needed
 	when supports dual-role mode.
+	it's considered valid for compatibility reasons, not allowed for
+	new bindings, and use "usb-role-switch" property instead.
  - vbus-supply : reference to the VBUS regulator, needed when supports
 	dual-role mode.
+	it's considered valid for compatibility reasons, not allowed for
+	new bindings, and put into a usb-connector node.
+	see connector/usb-connector.txt.
  - pinctrl-names : a pinctrl state named "default" is optional, and need be
 	defined if auto drd switch is enabled, that means the property dr_mode
 	is set as "otg", and meanwhile the property "mediatek,enable-manual-drd"
@@ -39,6 +44,8 @@ Optional properties:
 
  - maximum-speed : valid arguments are "super-speed", "high-speed" and
 	"full-speed"; refer to usb/generic.txt
+ - usb-role-switch : use USB Role Switch to support dual-role switch, but
+	not extcon; see usb/generic.txt.
  - enable-manual-drd : supports manual dual-role switch via debugfs; usually
 	used when receptacle is TYPE-A and also wants to support dual-role
 	mode.
@@ -61,6 +68,9 @@ The xhci should be added as subnode to mtu3 as shown in the following example
 if host mode is enabled. The DT binding details of xhci can be found in:
 Documentation/devicetree/bindings/usb/mediatek,mtk-xhci.txt
 
+The port would be added as subnode if use "usb-role-switch" property.
+	see graph.txt
+
 Example:
 ssusb: usb@11271000 {
 	compatible = "mediatek,mt8173-mtu3";