dt-bindings: phy: tegra-xusb: Add usb-role-switch

Add usb-role-switch property for Tegra210 and Tegra186 platforms. This
entry is used by XUSB pad controller driver to register for role changes
for OTG/Peripheral capable USB 2 ports.

Signed-off-by: Nagarjuna Kristam <[e-mail]>
Acked-by: Thierry Reding <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Signed-off-by: Thierry Reding <[e-mail]>

Documentation/devicetree/bindings/phy/nvidia,tegra124-xusb-padctl.txt

···
   - "device": for USB device mode
   - "otg": for USB OTG mode
 
+Required properties for OTG/Peripheral capable USB2 ports:
+- usb-role-switch: Boolean property to indicate that the port support OTG or
+  peripheral mode. If present, the port supports switching between USB host
+  and peripheral roles. Connector should be added as subnode.
+  See usb/usb-conn-gpio.txt.
+
 Optional properties:
 - nvidia,internal: A boolean property whose presence determines that a port
   is internal. In the absence of this property the port is considered to be