clk: max77802: Add DT binding documentation

Binding for Maxim MAX77802 32k clock generator block

This is a part of device tree bindings of MAX77802 multi-function device.

More information can be found in bindings/mfd/max77802.txt file.

The MAX77802 contains two 32.768khz clock outputs that can be controlled

(gated/ungated) over I2C.

Following properties should be present in main device node of the MFD chip.

Required properties:

- #clock-cells: From common clock binding; shall be set to 1.

Optional properties:

- clock-output-names: From common clock binding.

Each clock is assigned an identifier and client nodes can use this identifier

to specify the clock which they consume. Following indices are allowed:

     - 0: 32khz_ap clock,

     - 1: 32khz_cp clock.

Clocks are defined as preprocessor macros in dt-bindings/clock/maxim,max77802.h

header and can be used in device tree sources.

Example: Node of the MFD chip

	max77802: max77802@09 {

		compatible = "maxim,max77802";

		interrupt-parent = <&wakeup_eint>;

		interrupts = <26 0>;

		reg = <0x09>;

		#clock-cells = <1>;

		/* ... */

	};

Example: Clock consumer node

	foo@0 {

		compatible = "bar,foo";

		/* ... */

		clock-names = "my-clock";

		clocks = <&max77802 MAX77802_CLK_32K_AP>;

	};