* Maxim DS3231 Real Time Clock

Required properties:
see: Documentation/devicetree/bindings/i2c/trivial-devices.txt

Optional property:
- #clock-cells: Should be 1.
- clock-output-names:
  overwrite the default clock names "ds3231_clk_sqw" and "ds3231_clk_32khz".

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: square-wave output on the SQW pin
    - 1: square-wave output on the 32kHz pin

- interrupts: rtc alarm/event interrupt. When this property is selected,
  clock on the SQW pin cannot be used.

Example:

ds3231: ds3231@51 {
	compatible = "maxim,ds3231";
	reg = <0x68>;
	#clock-cells = <1>;
};

device1 {
...
	clocks = <&ds3231 0>;
...
};

device2 {
...
	clocks = <&ds3231 1>;
...
};