Spreadtrum SC2703 battery charger binding

Required properties:
 - compatible: Should be "sprd,sc2703-charger".
 - reg: Address offset of charger register.
 - phys: Contains a phandle to the USB phy.
 - vddvbus: Provide a handle to the usb module to operate vbus otg.
Optional Properties:
- monitored-battery: phandle of battery characteristics devicetree node.
  The charger uses the following battery properties:
- charge-term-current-microamp: current for charge termination phase.
- constant-charge-voltage-max-microvolt: maximum constant input voltage.
  See Documentation/devicetree/bindings/power/supply/battery.txt
- sprd,long-key-detection: the long key power on configuration option, if
  configured, press 15s the internal battery will disconnect.

Example:

	bat: battery {
		compatible = "simple-battery";
		charge-term-current-microamp = <120000>;
		constant-charge-voltage-max-microvolt = <4350000>;
		......
	};

	sc2703-charger {
		compatible = "sprd,sc2703-charger";
		reg = <0x4c>;
		phys = <&ssphy>;
		monitored-battery = <&bat>;
		sprd,long-key-detection;
		vddvbus:otg-vbus {
			regulator-name = "vddvbus";
			regulator-ramp-delay = <25000>;
		};
	};
