dt: binding documentation for bq2415x charger

Add devicetree binding documentation for bq2415x charger.
Signed-off-by: NSebastian Reichel <sre@debian.org>
Acked-by: NPavel Machek <pavel@ucw.cz>

Documentation/devicetree/bindings/power/bq2415x.txt

+Binding for TI bq2415x Li-Ion Charger
+
+Required properties:
+- compatible: Should contain one of the following:
+ * "ti,bq24150"
+ * "ti,bq24150"
+ * "ti,bq24150a"
+ * "ti,bq24151"
+ * "ti,bq24151a"
+ * "ti,bq24152"
+ * "ti,bq24153"
+ * "ti,bq24153a"
+ * "ti,bq24155"
+ * "ti,bq24156"
+ * "ti,bq24156a"
+ * "ti,bq24158"
+- reg:			   integer, i2c address of the device.
+- ti,current-limit:	   integer, initial maximum current charger can pull
+			   from power supply in mA.
+- ti,weak-battery-voltage: integer, weak battery voltage threshold in mV.
+			   The chip will use slow precharge if battery voltage
+			   is below this value.
+- ti,battery-regulation-voltage: integer, maximum charging voltage in mV.
+- ti,charge-current:	   integer, maximum charging current in mA.
+- ti,termination-current:  integer, charge will be terminated when current in
+			   constant-voltage phase drops below this value (in mA).
+- ti,resistor-sense:	   integer, value of sensing resistor in milliohm.
+
+Optional properties:
+- ti,usb-charger-detection: phandle to usb charger detection device.
+			    (required for auto mode)
+
+Example from Nokia N900:
+
+bq24150a {
+	compatible = "ti,bq24150a";
+	reg = <0x6b>;
+
+	ti,current-limit = <100>;
+	ti,weak-battery-voltage = <3400>;
+	ti,battery-regulation-voltage = <4200>;
+	ti,charge-current = <650>;
+	ti,termination-current = <100>;
+	ti,resistor-sense = <68>;
+
+	ti,usb-charger-detection = <&isp1704>;
+};