usb: phy: nop: device tree documentation for vbus

Enhance the phy documentation by adding 2 new optional bindings :
 - the vbus gpio, which detects usb insertion
 - the vbus regulator, which provides current drawn from the usb cable
Signed-off-by: NRobert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: NFelipe Balbi <balbi@ti.com>

Documentation/devicetree/bindings/usb/usb-nop-xceiv.txt

@@ -17,6 +17,11 @@ Optional properties:
 
 - reset-gpios: Should specify the GPIO for reset.
 
+- vbus-detect-gpio: should specify the GPIO detecting a VBus insertion
+                    (see Documentation/devicetree/bindings/gpio/gpio.txt)
+- vbus-regulator : should specifiy the regulator supplying current drawn from
+  the VBus line (see Documentation/devicetree/bindings/regulator/regulator.txt).
+
 Example:
 
 	hsusb1_phy {
@@ -26,8 +31,11 @@ Example:
 		clock-names = "main_clk";
 		vcc-supply = <&hsusb1_vcc_regulator>;
 		reset-gpios = <&gpio1 7 GPIO_ACTIVE_LOW>;
+		vbus-detect-gpio = <&gpio2 13 GPIO_ACTIVE_HIGH>;
+		vbus-regulator = <&vbus_regulator>;
 	};
 
 hsusb1_phy is a NOP USB PHY device that gets its clock from an oscillator
 and expects that clock to be configured to 19.2MHz by the NOP PHY driver.
 hsusb1_vcc_regulator provides power to the PHY and GPIO 7 controls RESET.
+GPIO 13 detects VBus insertion, and accordingly notifies the vbus-regulator.