[nrf fromlist] tests: adc: Add overlay for nRF54L15 PDK for adc_api test

New file to make test works.

Upstream PR: zephyrproject-rtos/zephyr#68692

Signed-off-by: Karol Lasończyk <karol.lasonczyk@nordicsemi.no>

tests/drivers/adc/adc_api/boards/nrf54l15pdk_nrf54l15_cpuapp.overlay

@@ -0,0 +1,34 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Copyright (c) 2024 Nordic Semiconductor ASA
+ */
+
+/ {
+	zephyr,user {
+		io-channels = <&adc 0>, <&adc 2>;
+	};
+};
+
+&adc {
+	#address-cells = <1>;
+	#size-cells = <0>;
+
+	channel@0 {
+		reg = <0>;
+		zephyr,gain = "ADC_GAIN_1";
+		zephyr,reference = "ADC_REF_INTERNAL";
+		zephyr,acquisition-time = <ADC_ACQ_TIME(ADC_ACQ_TIME_MICROSECONDS, 10)>;
+		zephyr,input-positive = <NRF_SAADC_AIN1>;
+		zephyr,resolution = <10>;
+	};
+
+	channel@2 {
+		reg = <2>;
+		zephyr,gain = "ADC_GAIN_1";
+		zephyr,reference = "ADC_REF_INTERNAL";
+		zephyr,acquisition-time = <ADC_ACQ_TIME(ADC_ACQ_TIME_MICROSECONDS, 10)>;
+		zephyr,input-positive = <NRF_SAADC_AIN2>;
+		zephyr,resolution = <10>;
+	};
+};