Binding for Maxim MAX77686 32k clock generator block

This is a part of device tree bindings of MAX77686 multi-function device.
More information can be found in bindings/mfd/max77686.txt file.

The MAX77686 contains three 32.768khz clock outputs that can be controlled
(gated/ungated) over I2C.

Following properties should be presend 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,
    - 2: 32khz_pmic clock.

Clocks are defined as preprocessor macros in dt-bindings/clock/maxim,max77686.h
header and can be used in device tree sources.

Example: Node of the MFD chip

	max77686: max77686@09 {
		compatible = "maxim,max77686";
		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 = <&max77686 MAX77686_CLK_PMIC>;
	};
