Binding for Maxim MAX77686/MAX77802 32k clock generator block

This is a part of device tree bindings of MAX77686/MAX77802 multi-function
device. More information can be found in bindings/mfd/max77686.txt file for
MAX77686 and bindings/mfd/max77802.txt for MAX77802.

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

The MAX77802 contains two 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 (max77686, max77802),
    - 1: 32khz_cp clock (max77686, max77802),
    - 2: 32khz_pmic clock (max77686).

Clocks are defined as preprocessor macros in dt-bindings/clock/maxim,max77686.h
header for MAX77686 and dt-bindings/clock/maxim,max77802.h for MAX77802 and can
be used in device tree sources.

Example:

1. With MAX77686:

#include <dt-bindings/clock/maxim,max77686.h>
/* ... */

	Node of the MFD chip
		max77686: max77686@09 {
			compatible = "maxim,max77686";
			interrupt-parent = <&wakeup_eint>;
			interrupts = <26 0>;
			reg = <0x09>;
			#clock-cells = <1>;

			/* ... */
		};

	Clock consumer node

		foo@0 {
			compatible = "bar,foo";
			/* ... */
			clock-names = "my-clock";
			clocks = <&max77686 MAX77686_CLK_PMIC>;
		};

2. With MAX77802:

#include <dt-bindings/clock/maxim,max77802.h>
/* ... */

	Node of the MFD chip
		max77802: max77802@09 {
			compatible = "maxim,max77802";
			interrupt-parent = <&wakeup_eint>;
			interrupts = <26 0>;
			reg = <0x09>;
			#clock-cells = <1>;

			/* ... */
		};

	Clock consumer node

		foo@0 {
			compatible = "bar,foo";
			/* ... */
			clock-names = "my-clock";
			clocks = <&max77802 MAX77802_CLK_32K_AP>;
		};