ARM: dts: mxs: Add iio-hwmon to mx28 soc

This allows to read the SoC on-die temperature sensor available on the LRADC by
using:
 cat /sys/class/hwmon/hwmon0/device/temp1_input
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>

arch/arm/boot/dts/imx28.dtsi

@@ -1182,4 +1182,9 @@ etn_switch: switch@800f8000 {
 			status = "disabled";
 		};
 	};
+
+	iio_hwmon {
+		compatible = "iio-hwmon";
+		io-channels = <&lradc 8>;
+	};
 };