devicetree: bindings: document lsi,zevio-usb

Add documentation for zevio-usb
Signed-off-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Daniel Tang <dt.tangr@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/usb/ci-hdrc-zevio.txt

+* LSI Zevio USB OTG Controller
+
+Required properties:
+- compatible: Should be "lsi,zevio-usb"
+- reg: Should contain registers location and length
+- interrupts: Should contain controller interrupt
+
+Optional properties:
+- vbus-supply: regulator for vbus
+
+Examples:
+		usb0: usb@b0000000 {
+			reg = <0xb0000000 0x1000>;
+			compatible = "lsi,zevio-usb";
+			interrupts = <8>;
+			vbus-supply = <&vbus_reg>;
+		};