mfd: Add DT binding for Maxim MAX77802 IC

The MAX77802 is a chip that contains regulators, 2 32kHz clocks,
a RTC and an I2C interface to program the individual components.

The are already DT bindings for the regulators and clocks and
these reference to a bindings/mfd/max77802.txt file, that didn't
exist, for the details about the PMIC.

Signed-off-by: Javier Martinez Canillas <[e-mail]>
Reviewed-by: Krzysztof Kozlowski <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>

Documentation/devicetree/bindings/mfd/max77802.txt

···
+Maxim MAX77802 multi-function device
+
+The Maxim MAX77802 is a Power Management IC (PMIC) that contains 10 high
+efficiency Buck regulators, 32 Low-DropOut (LDO) regulators used to power
+up application processors and peripherals, a 2-channel 32kHz clock outputs,
+a Real-Time-Clock (RTC) and a I2C interface to program the individual
+regulators, clocks outputs and the RTC.
+
+Bindings for the built-in 32k clock generator block and
+regulators are defined in ../clk/maxim,max77802.txt and
+../regulator/max77802.txt respectively.
+
+Required properties:
+- compatible		: Must be "maxim,max77802"
+- reg			: Specifies the I2C slave address of PMIC block.
+- interrupts		: I2C device IRQ line connected to the main SoC.
+- interrupt-parent	: The parent interrupt controller.
+
+Example:
+
+	max77802: pmic@09 {
+		compatible = "maxim,max77802";
+		interrupt-parent = <&intc>;
+		interrupts = <26 IRQ_TYPE_NONE>;
+		reg = <0x09>;
+	};