power: da9150: Add DT binding documentation for charger

Signed-off-by: Adam Thomson <Adam.Thomson.Opensource@diasemi.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>

Documentation/devicetree/bindings/power/da9150-charger.txt

+Dialog Semiconductor DA9150 Charger Power Supply bindings
+
+Required properties:
+- compatible: "dlg,da9150-charger" for DA9150 Charger Power Supply
+
+Optional properties:
+- io-channels: List of phandle and IIO specifier pairs
+- io-channel-names: List of channel names used by charger
+      ["CHAN_IBUS", "CHAN_VBUS", "CHAN_TJUNC", "CHAN_VBAT"]
+  (See Documentation/devicetree/bindings/iio/iio-bindings.txt for further info)
+
+
+Example:
+
+	da9150-charger {
+		compatible = "dlg,da9150-charger";
+
+		io-channels = <&gpadc 0>,
+			      <&gpadc 2>,
+			      <&gpadc 8>,
+			      <&gpadc 5>;
+		io-channel-names = "CHAN_IBUS",
+				   "CHAN_VBUS",
+				   "CHAN_TJUNC",
+				   "CHAN_VBAT";
+	};