ARM: dts: meson: move iio-hwmon for the SoC temperature to meson.dtsi

The SoC temperature can be retrieved from ADC channel 8 on all 32-bit
SoCs (Meson6, Meson8, Meson8b and Meson8m2). Move the iio-hwmon instance
to meson.dtsi instead of duplicating it in all board.dts.
If the temperature sensor calibration data is missing for a board then
iio-hwmon will simply not probe.

Signed-off-by: Martin Blumenstingl <[e-mail]>
Reviewed-by: Neil Armstrong <[e-mail]>
Signed-off-by: Kevin Hilman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/arm/boot/dts/meson.dtsi

···
 	#size-cells = <1>;
 	interrupt-parent = <&gic>;
 
+	iio-hwmon {
+		compatible = "iio-hwmon";
+		io-channels = <&saradc 8>;
+	};
+
 	soc {
 		compatible = "simple-bus";
 		#address-cells = <1>;

arch/arm/boot/dts/meson8b-ec100.dts

···
 		timeout-ms = <20000>;
 	};
 
-	iio-hwmon {
-		compatible = "iio-hwmon";
-		io-channels = <&saradc 8>;
-	};
-
 	leds {
 		compatible = "gpio-leds";
 

arch/arm/boot/dts/meson8b-mxq.dts

···
 		reg = <0x40000000 0x40000000>;
 	};
 
-	iio-hwmon {
-		compatible = "iio-hwmon";
-		io-channels = <&saradc 8>;
-	};
-
 	vcck: regulator-vcck {
 		compatible = "pwm-regulator";
 

arch/arm/boot/dts/meson8b-odroidc1.dts

···
 			  1800000 1>;
 	};
 
-	iio-hwmon {
-		compatible = "iio-hwmon";
-		io-channels = <&saradc 8>;
-	};
-
 	rtc32k_xtal: rtc32k-xtal-clk {
 		/* X3 in the schematics */
 		compatible = "fixed-clock";

arch/arm/boot/dts/meson8m2-mxiii-plus.dts

···
 		};
 	};
 
-	iio-hwmon {
-		compatible = "iio-hwmon";
-		io-channels = <&saradc 8>;
-	};
-
 	vcc_3v3: regulator-vcc3v3 {
 		compatible = "regulator-fixed";
 		regulator-name = "VCC3V3";