ARM: dts: exynos: Enable ADC on Arndale Octa

Arndale Octa (Exynos5420) has two ADC pins (AIN0 and AIN1) exposed on
CON6 header pins.  Add ADC node to DTS file to enable it.
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>

arch/arm/boot/dts/exynos5420-arndale-octa.dts

@@ -51,6 +51,11 @@ wakeup {
 	};
 };
 
+&adc {
+	vdd-supply = <&ldo4_reg>;
+	status = "okay";
+};
+
 &cci {
 	status = "disabled";
 };