samples: adc: add support for gd32a503v_eval board.

add support for gd32a503v_eval board.

Signed-off-by: YuLong Yao <[email protected]>

Author: feilongfl

samples/drivers/adc/boards/gd32a503v_eval.overlay

@@ -0,0 +1,27 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Copyright (c) 2023 YuLong Yao <[email protected]>
+ */
+
+#include <zephyr/dt-bindings/adc/adc.h>
+
+/ {
+	zephyr,user {
+		/* adjust channel number according to pinmux in board.dts */
+		io-channels = <&adc0 1>;
+	};
+};
+
+&adc0 {
+	#address-cells = <1>;
+	#size-cells = <0>;
+
+	channel@1 {
+		reg = <1>;
+		zephyr,gain = "ADC_GAIN_1";
+		zephyr,reference = "ADC_REF_INTERNAL";
+		zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
+		zephyr,resolution = <12>;
+	};
+};