AXP family PMIC device tree bindings

The axp20x family current members :
axp202 (X-Powers)
axp209 (X-Powers)
axp221 (X-Powers)

Required properties:
- compatible: "x-powers,axp202", "x-powers,axp209", "x-powers,axp221"
- reg: The I2C slave address for the AXP chip
- interrupt-parent: The parent interrupt controller
- interrupts: SoC NMI / GPIO interrupt connected to the PMIC's IRQ pin
- interrupt-controller: The PMIC has its own internal IRQs
- #interrupt-cells: Should be set to 1

Optional properties:
- x-powers,dcdc-freq: defines the work frequency of DC-DC in KHz
		      (range: 750-1875). Default: 1.5MHz
- <input>-supply: a phandle to the regulator supply node. May be omitted if
		  inputs are unregulated, such as using the IPSOUT output
		  from the PMIC.

- regulators: A node that houses a sub-node for each regulator. Regulators
	      not used but preferred to be managed by the OS should be
	      listed as well.
	      See Documentation/devicetree/bindings/regulator/regulator.txt
	      for more information on standard regulator bindings.

Optional properties for DCDC regulators:
- x-powers,dcdc-workmode: 1 for PWM mode, 0 for AUTO (PWM/PFM) mode
			  Default: Current hardware setting
			  The DCDC regulators work in a mixed PWM/PFM mode,
			  using PFM under light loads and switching to PWM
			  for heavier loads. Forcing PWM mode trades efficiency
			  under light loads for lower output noise. This
			  probably makes sense for HiFi audio related
			  applications that aren't battery constrained.


AXP202/AXP209 regulators, type, and corresponding input supply names:

Regulator	  Type		  Supply Name		  Notes
---------	  ----		  -----------		  -----
DCDC2		: DC-DC buck	: vin2-supply
DCDC3		: DC-DC	buck	: vin3-supply
LDO1		: LDO		: acin-supply		: always on
LDO2		: LDO		: ldo24in-supply	: shared supply
LDO3		: LDO		: ldo3in-supply
LDO4		: LDO		: ldo24in-supply	: shared supply
LDO5		: LDO		: ldo5in-supply

AXP221 regulators, type, and corresponding input supply names:

Regulator	  Type		  Supply Name		  Notes
---------	  ----		  -----------		  -----
DCDC1		: DC-DC buck	: vin1-supply
DCDC2		: DC-DC buck	: vin2-supply
DCDC3		: DC-DC	buck	: vin3-supply
DCDC4		: DC-DC	buck	: vin4-supply
DCDC5		: DC-DC	buck	: vin5-supply
DC1SW		: On/Off Switch	: dcdc1-supply		: DCDC1 secondary output
DC5LDO		: LDO		: dcdc5-supply		: input from DCDC5
ALDO1		: LDO		: aldoin-supply		: shared supply
ALDO2		: LDO		: aldoin-supply		: shared supply
ALDO3		: LDO		: aldoin-supply		: shared supply
DLDO1		: LDO		: dldoin-supply		: shared supply
DLDO2		: LDO		: dldoin-supply		: shared supply
DLDO3		: LDO		: dldoin-supply		: shared supply
DLDO4		: LDO		: dldoin-supply		: shared supply
ELDO1		: LDO		: eldoin-supply		: shared supply
ELDO2		: LDO		: eldoin-supply		: shared supply
ELDO3		: LDO		: eldoin-supply		: shared supply
LDO_IO0		: LDO		: ips-supply		: GPIO 0
LDO_IO1		: LDO		: ips-supply		: GPIO 1
RTC_LDO		: LDO		: ips-supply		: always on

Example:

axp209: pmic@34 {
	compatible = "x-powers,axp209";
	reg = <0x34>;
	interrupt-parent = <&nmi_intc>;
	interrupts = <0 IRQ_TYPE_LEVEL_LOW>;
	interrupt-controller;
	#interrupt-cells = <1>;

	regulators {
		x-powers,dcdc-freq = <1500>;

		vdd_cpu: dcdc2 {
			regulator-always-on;
			regulator-min-microvolt = <1000000>;
			regulator-max-microvolt = <1450000>;
			regulator-name = "vdd-cpu";
		};

		vdd_int_dll: dcdc3 {
			regulator-always-on;
			regulator-min-microvolt = <1000000>;
			regulator-max-microvolt = <1400000>;
			regulator-name = "vdd-int-dll";
		};

		vdd_rtc: ldo1 {
			regulator-always-on;
			regulator-min-microvolt = <1200000>;
			regulator-max-microvolt = <1400000>;
			regulator-name = "vdd-rtc";
		};

		avcc: ldo2 {
			regulator-always-on;
			regulator-min-microvolt = <2700000>;
			regulator-max-microvolt = <3300000>;
			regulator-name = "avcc";
		};

		ldo3 {
			/* unused but preferred to be managed by OS */
		};
	};
};
