Spreadtrum SC2731 PMIC battery charger binding

Required properties:
 - compatible: Should be "sprd,sc2731-charger".
 - reg: Address offset of charger register.
 - phys: Contains a phandle to the USB phy.

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

Example:

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

	sc2731_pmic: pmic@0 {
		compatible = "sprd,sc2731";
		reg = <0>;
		spi-max-frequency = <26000000>;
		interrupts = <GIC_SPI 31 IRQ_TYPE_LEVEL_HIGH>;
		interrupt-controller;
		#interrupt-cells = <2>;
		#address-cells = <1>;
		#size-cells = <0>;

		charger@0 {
			compatible = "sprd,sc2731-charger";
			reg = <0x0>;
			phys = <&ssphy>;
			monitored-battery = <&bat>;
		};
	};
