Documentation: mfd: Add binding document for S2MPA01

* Samsung S2MPA01 Voltage and Current Regulator

The Samsung S2MPA01 is a multi-function device which includes high

efficiency buck converters including Dual-Phase buck converter, various LDOs,

and an RTC. It is interfaced to the host controller using an I2C interface.

Each sub-block is addressed by the host system using different I2C slave

addresses.

Required properties:

- compatible: Should be "samsung,s2mpa01-pmic".

- reg: Specifies the I2C slave address of the PMIC block. It should be 0x66.

Optional properties:

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

  the interrupts from s2mpa01 are delivered to.

- interrupts: An interrupt specifier for the sole interrupt generated by the

  device.

Optional nodes:

- regulators: The regulators of s2mpa01 that have to be instantiated should be

  included in a sub-node named 'regulators'. Regulator nodes and constraints

  included in this sub-node use the standard regulator bindings which are

  documented elsewhere.

Properties for BUCK regulator nodes:

- regulator-ramp-delay: ramp delay in uV/us. May be 6250, 12500

  (default), 25000, or 50000. May be 0 for disabling the ramp delay on

  BUCK{1,2,3,4}.

 In the absence of the regulator-ramp-delay property, the default ramp

 delay will be used.

  NOTE: Some BUCKs share the ramp rate setting i.e. same ramp value will be set

  for a particular group of BUCKs. So provide same regulator-ramp-delay=<value>.

  The following BUCKs share ramp settings:

  * 1 and 6

  * 2 and 4

  * 8, 9, and 10

The following are the names of the regulators that the s2mpa01 PMIC block

supports. Note: The 'n' in LDOn and BUCKn represents the LDO or BUCK number

as per the datasheet of s2mpa01.

	- LDOn

		  - valid values for n are 1 to 26

		  - Example: LDO1, LD02, LDO26

	- BUCKn

		  - valid values for n are 1 to 10.

		  - Example: BUCK1, BUCK2, BUCK9

Example:

	s2mpa01_pmic@66 {

		compatible = "samsung,s2mpa01-pmic";

		reg = <0x66>;

		regulators {

			ldo1_reg: LDO1 {

				regulator-name = "VDD_ALIVE";

				regulator-min-microvolt = <1000000>;

				regulator-max-microvolt = <1000000>;

			};

			ldo2_reg: LDO2 {

				regulator-name = "VDDQ_MMC2";

				regulator-min-microvolt = <2800000>;

				regulator-max-microvolt = <2800000>;

				regulator-always-on;

			};

			buck1_reg: BUCK1 {

				regulator-name = "vdd_mif";

				regulator-min-microvolt = <950000>;

				regulator-max-microvolt = <1350000>;

				regulator-always-on;

				regulator-boot-on;

			};

			buck2_reg: BUCK2 {

				regulator-name = "vdd_arm";

				regulator-min-microvolt = <950000>;

				regulator-max-microvolt = <1350000>;

				regulator-always-on;

				regulator-boot-on;

				regulator-ramp-delay = <50000>;

			};

		};

	};