ARM: dts: stm32: enable ADC on stm32f429i-eval board

Enable analog to digital converter on stm32f429i-eval board.
It has on-board potentimeter wired to ADC3 in8 analog pin and
uses fixed regulator to provide reference voltage.
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Signed-off-by: Alexandre TORGUE <alexandre.torgue@st.com>

arch/arm/boot/dts/stm32429i-eval.dts

@@ -70,6 +70,20 @@ soc {
 		dma-ranges = <0xc0000000 0x0 0x10000000>;
 	};
 
+	regulators {
+		compatible = "simple-bus";
+		#address-cells = <1>;
+		#size-cells = <0>;
+
+		reg_vref: regulator@0 {
+			compatible = "regulator-fixed";
+			reg = <0>;
+			regulator-name = "vref";
+			regulator-min-microvolt = <3300000>;
+			regulator-max-microvolt = <3300000>;
+		};
+	};
+
 	leds {
 		compatible = "gpio-leds";
 		green {
@@ -112,6 +126,17 @@ usbotg_hs_phy: usbphy {
 	};
 };
 
+&adc {
+	pinctrl-names = "default";
+	pinctrl-0 = <&adc3_in8_pin>;
+	vref-supply = <&reg_vref>;
+	status = "okay";
+	adc3: adc@200 {
+		st,adc-channels = <8>;
+		status = "okay";
+	};
+};
+
 &clk_hse {
 	clock-frequency = <25000000>;
 };