mfd: da9055: Add DT binding documentation for PMIC

* Dialog DA9055 Power Management Integrated Circuit (PMIC)

DA9055 consists of a large and varied group of sub-devices (I2C Only):

Device			 Supply Names	 Description

------			 ------------	 -----------

da9055-gpio		:		: GPIOs

da9055-regulator	:		: Regulators

da9055-onkey		:		: On key

da9055-rtc		:		: RTC

da9055-hwmon		:		: ADC

da9055-watchdog		:		: Watchdog

The CODEC device in DA9055 has a separate, configurable I2C address and so

is instantiated separately from the PMIC.

For details on accompanying CODEC I2C device, see the following:

Documentation/devicetree/bindings/sound/da9055.txt

======

Required properties:

- compatible : Should be "dlg,da9055-pmic"

- reg: Specifies the I2C slave address (defaults to 0x5a but can be modified)

- interrupt-parent: Specifies the phandle of the interrupt controller to which

  the IRQs from da9055 are delivered to.

- interrupts: IRQ line info for da9055 chip.

- interrupt-controller: da9055 has internal IRQs (has own IRQ domain).

- #interrupt-cells: Should be 1, is the local IRQ number for da9055.

Sub-nodes:

- regulators : Contain the regulator nodes. The DA9055 regulators are

  bound using their names as listed below:

    buck1     : regulator BUCK1

    buck2     : regulator BUCK2

    ldo1      : regulator LDO1

    ldo2      : regulator LDO2

    ldo3      : regulator LDO3

    ldo4      : regulator LDO4

    ldo5      : regulator LDO5

    ldo6      : regulator LDO6

  The bindings details of individual regulator device can be found in:

  Documentation/devicetree/bindings/regulator/regulator.txt

Example:

	pmic: da9055-pmic@5a {

		compatible = "dlg,da9055-pmic";

		reg = <0x5a>;

		interrupt-parent = <&intc>;

		interrupts = <5 IRQ_TYPE_LEVEL_LOW>;

		interrupt-controller;

		#interrupt-cells = <1>;

		regulators {

			buck1: BUCK1 {

				regulator-min-microvolt = <725000>;

				regulator-max-microvolt = <2075000>;

			};

			buck2: BUCK2 {

				regulator-min-microvolt = <925000>;

				regulator-max-microvolt = <2500000>;

			};

			ldo1: LDO1 {

				regulator-min-microvolt = <900000>;

				regulator-max-microvolt = <3300000>;

			};

		};

	};