variant: Adds support for Arduino Uno R4.

A new configuration method has been adopted, allowing support to be added
with less configuration than before.

Signed-off-by: TOKITA Hiroshi <tokita.hiroshi@gmail.com>

Author: soburi

variants/arduino_uno_r4_r7fa4m1ab3cfm/arduino_uno_r4_r7fa4m1ab3cfm.overlay

@@ -0,0 +1,65 @@
+/*
+ * Copyright (c) 2026 TOKITA Hiroshi
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+&adc0 {
+	status = "okay";
+	#address-cells = <1>;
+	#size-cells = <0>;
+
+	channel@0 {
+		reg = <0x0>;
+		zephyr,gain = "ADC_GAIN_1";
+		zephyr,reference = "ADC_REF_VDD_1";
+		zephyr,resolution = <12>;
+		zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
+		zephyr,vref-mv = <5000>;
+	};
+
+	channel@1 {
+		reg = <0x1>;
+		zephyr,gain = "ADC_GAIN_1";
+		zephyr,reference = "ADC_REF_VDD_1";
+		zephyr,resolution = <12>;
+		zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
+		zephyr,vref-mv = <5000>;
+	};
+
+	channel@2 {
+		reg = <0x2>;
+		zephyr,gain = "ADC_GAIN_1";
+		zephyr,reference = "ADC_REF_VDD_1";
+		zephyr,resolution = <12>;
+		zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
+		zephyr,vref-mv = <5000>;
+	};
+
+	channel@9 {
+		reg = <0x9>;
+		zephyr,gain = "ADC_GAIN_1";
+		zephyr,reference = "ADC_REF_VDD_1";
+		zephyr,resolution = <12>;
+		zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
+		zephyr,vref-mv = <5000>;
+	};
+
+	channel@15 {
+		reg = <0x15>;
+		zephyr,gain = "ADC_GAIN_1";
+		zephyr,reference = "ADC_REF_VDD_1";
+		zephyr,resolution = <12>;
+		zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
+		zephyr,vref-mv = <5000>;
+	};
+
+	channel@16 {
+		reg = <0x16>;
+		zephyr,gain = "ADC_GAIN_1";
+		zephyr,reference = "ADC_REF_VDD_1";
+		zephyr,resolution = <12>;
+		zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
+		zephyr,vref-mv = <5000>;
+	};
+};

variants/arduino_uno_r4_r7fa4m1ab3cfm/variant.h

@@ -0,0 +1,5 @@
+/*
+ * Copyright (c) 2026 TOKITA Hiroshi
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */