hwmon: (sht15) Add device tree support

Allow the driver to work with device tree support.

Based on initial patch submission from Peter Fox.

Tested on a imx7d-sdb board connected to a SHT15 board via Mikro Bus.

Signed-off-by: Marco Franchi <marco.franchi@nxp.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/devicetree/bindings/hwmon/sht15.txt

@@ -0,0 +1,19 @@
+Sensirion SHT15 Humidity and Temperature Sensor
+
+Required properties:
+
+ - "compatible": must be "sensirion,sht15".
+ - "data-gpios": GPIO connected to the data line.
+ - "clk-gpios": GPIO connected to the clock line.
+ - "vcc-supply": regulator that drives the VCC pin.
+
+Example:
+
+	sensor {
+		pinctrl-names = "default";
+		pinctrl-0 = <&pinctrl_sensor>;
+		compatible = "sensirion,sht15";
+		clk-gpios = <&gpio4 12 0>;
+		data-gpios = <&gpio4 13 0>;
+		vcc-supply = <&reg_sht15>;
+	};