samples: drivers: adc: Add tests support for ADC driver on EK-RA2A1 board

Add Renesas EK-RA2A1 board support for sample:

- samples/drivers/adc/adc_dt

Signed-off-by: Thinh Le Cong <[email protected]>

Author: Thinh Le Cong

samples/drivers/adc/adc_dt/boards/ek_ra2a1.overlay

@@ -0,0 +1,54 @@
+/*
+ * Copyright (c) 2025 Renesas Electronics Corporation
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/ {
+	zephyr,user {
+		io-channels = <&adc0 0>, <&adc0 1>;
+	};
+};
+
+&pinctrl {
+	adc0_default: adc0_default {
+		group1 {
+			/* input */
+			psels = <RA_PSEL(RA_PSEL_ADC, 5, 0)>,
+				<RA_PSEL(RA_PSEL_ADC, 5, 1)>;
+			renesas,analog-enable;
+		};
+	};
+};
+
+&adc0 {
+	status = "okay";
+	#address-cells = <1>;
+	#size-cells = <0>;
+	interrupts = <31 1>;
+	interrupt-names = "scanend";
+
+	/*
+	 * Channel 0 is used in single ended mode, with 15 bit resolution
+	 */
+	channel@0 {
+		reg = <0>;
+		zephyr,gain = "ADC_GAIN_1";
+		zephyr,reference = "ADC_REF_EXTERNAL0";
+		zephyr,resolution = <15>;
+		zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
+		zephyr,vref-mv = <3300>;
+	};
+
+	/*
+	 * Channel 1 is used in single ended mode, with 15 bit resolution
+	 */
+	channel@1 {
+		reg = <1>;
+		zephyr,gain = "ADC_GAIN_1";
+		zephyr,reference = "ADC_REF_EXTERNAL0";
+		zephyr,resolution = <15>;
+		zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
+		zephyr,vref-mv = <3300>;
+	};
+};

samples/drivers/adc/adc_dt/src/main.c

@@ -38,6 +38,9 @@ int main(void)
 		.buffer = &buf,
 		/* buffer size in bytes, not number of samples */
 		.buffer_size = sizeof(buf),
+#if DT_HAS_COMPAT_STATUS_OKAY(renesas_ra_adc_16)
+		.calibrate = true,
+#endif
 	};
 
 	/* Configure channels individually prior to sampling. */