dt-bindings: w1: document bindings for ds2760 battery monitor

Devicetree bindings for Maxim DS2760

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The ds2760 is a w1 slave device and must hence have its sub-node in DT

under a w1 bus master node.

The device exposes a power supply, so the details described in

Documentation/devicetree/bindings/power/supply/power_supply.txt apply.

Required properties:

- compatible: must be "maxim,ds2760"

Optional properties:

- power-supplies:	Refers to one or more power supplies connected to

			this battery.

- maxim,pmod-enabled:	This boolean property enables the DS2760 to enter

			sleep mode when the DQ line goes low for greater

			than 2 seconds and leave sleep Mode when the DQ

			line goes high.

- maxim,cache-time-ms:	Time im milliseconds to cache the data for. When

			this time expires, the values are read again from

			the hardware. Defaults to 1000.

- rated-capacity-microamp-hours:

			The rated capacity of the battery, in mAh.

			If not specified, the value stored in the

			non-volatile chip memory is used.