Documentation: dt-bindings: trickle charger dt binding document for ds1339

Some DS13XX devices have "trickle chargers".  Introduce a device tree
binding for the resistor and diode configuration for enabling trickle
charger.

Signed-off-by: Matti Vaittinen <matti.vaittinen@nsn.com>
Acked-by: Jason Cooper <jason@lakedaemon.net>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Pavel Machek <pavel@denx.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/devicetree/bindings/rtc/dallas,ds1339.txt

@@ -0,0 +1,18 @@
+* Dallas DS1339		I2C Serial Real-Time Clock
+
+Required properties:
+- compatible: Should contain "dallas,ds1339".
+- reg: I2C address for chip
+
+Optional properties:
+- trickle-resistor-ohms : Selected resistor for trickle charger
+	Values usable for ds1339 are 250, 2000, 4000
+	Should be given if trickle charger should be enabled
+- trickle-diode-disable : Do not use internal trickle charger diode
+	Should be given if internal trickle charger diode should be disabled
+Example:
+	ds1339: rtc@68 {
+		compatible = "dallas,ds1339";
+		trickle-resistor-ohms = <250>;
+		reg = <0x68>;
+	};