hwmon: (ad741x) Add DT bindings for Analog Devices AD741x

This adds device tree bindings for Analog Devices AD741x
as found in Gateway routers.

Cc: devicetree@vger.kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/devicetree/bindings/hwmon/ad741x.txt

+* AD7416/AD7417/AD7418 Temperature Sensor Device Tree Bindings
+
+Required properties:
+- compatible: one of
+		"adi,ad7416"
+		"adi,ad7417"
+		"adi,ad7418"
+- reg: I2C address
+
+Example:
+
+hwmon@28 {
+	compatible = "adi,ad7418";
+	reg = <0x28>;
+};