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

This patch adds the devicetree bindings for Maxim's ds2760 battery
monitors.
Signed-off-by: Daniel Mack <daniel@zonque.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>

Documentation/devicetree/bindings/power/supply/maxim,ds2760.txt

+Devicetree bindings for Maxim DS2760
+====================================
+
+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.