Spreadtrum SC2731 Voltage regulators

The SC2731 integrates low-voltage and low quiescent current DCDC/LDO.
14 LDO and 3 DCDCs are designed for external use. All DCDCs/LDOs have
their own bypass (power-down) control signals. External tantalum or MLCC
ceramic capacitors are recommended to use with these LDOs.

Required properties:
 - compatible: should be "sprd,sc27xx-regulator".

List of regulators provided by this controller. It is named according to
its regulator type, BUCK_<name> and LDO_<name>. The definition for each
of these nodes is defined using the standard binding for regulators at
Documentation/devicetree/bindings/regulator/regulator.txt.

The valid names for regulators are:
BUCK:
	BUCK_CPU0, BUCK_CPU1, BUCK_RF
LDO:
	LDO_CAMA0, LDO_CAMA1, LDO_CAMMOT, LDO_VLDO, LDO_EMMCCORE, LDO_SDCORE,
	LDO_SDIO, LDO_WIFIPA, LDO_USB33, LDO_CAMD0, LDO_CAMD1, LDO_CON,
	LDO_CAMIO, LDO_SRAM

Example:
	regulators {
		compatible = "sprd,sc27xx-regulator";

		vddarm0: BUCK_CPU0 {
			regulator-name = "vddarm0";
			regulator-min-microvolt = <400000>;
			regulator-max-microvolt = <1996875>;
			regulator-ramp-delay = <25000>;
			regulator-always-on;
		};

		vddcama0: LDO_CAMA0 {
			regulator-name = "vddcama0";
			regulator-min-microvolt = <1200000>;
			regulator-max-microvolt = <3750000>;
			regulator-enable-ramp-delay = <100>;
		};
		...
	};
