rtc: bq32000: add trickle charger device tree binding

BQ32000 have "trickle chargers".  Introduce a device tree binding for
specifying the trickle charger configuration for that.
Signed-off-by: NPavel Machek <pavel@denx.de>
Reviewed-by: NJason Cooper <jason@lakedameon.net>
Cc: Matti Vaittinen <matti.vaittinen@nsn.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Documentation/devicetree/bindings/i2c/ti,bq32k.txt

+* TI BQ32000                I2C Serial Real-Time Clock
+
+Required properties:
+- compatible: Should contain "ti,bq32000".
+- reg: I2C address for chip
+
+Optional properties:
+- trickle-resistor-ohms : Selected resistor for trickle charger
+       Values usable are 1120 and 20180
+       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:
+       bq32000: rtc@68 {
+               compatible = "ti,bq32000";
+               trickle-resistor-ohms = <1120>;
+               reg = <0x68>;
+       };