test: driver: uart: add silabs slwrb4180a overlay for async usart test

Add overlay for slwrb4180a board to test async silabs usart driver with
dma.

Signed-off-by: Martin Hoff <[email protected]>

tests/drivers/uart/uart_async_api/boards/slwrb4180a.overlay

@@ -0,0 +1,62 @@
+/*
+ * Copyright (c) 2025, Silicon Laboratories Inc.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/*
+ * Need to connect PC0 and PC1 of the Expension Pin header
+ */
+/ {
+	chosen {
+		zephyr,console = &usart1;
+		zephyr,shell-uart = &usart1;
+		zephyr,uart-pipe = &usart1;
+	};
+};
+
+&pinctrl{
+	usart0_default: usart0_default {
+		group0 {
+			pins = <USART0_TX_PC0>;
+			drive-push-pull;
+			output-high;
+		};
+		group1 {
+			pins = <USART0_RX_PC1>;
+			input-enable;
+			silabs,input-filter;
+		};
+	};
+	usart1_default: usart1_default {
+		group0 {
+			pins = <USART1_TX_PA5>;
+			drive-push-pull;
+			output-high;
+		};
+		group1 {
+			pins = <USART1_RX_PA6>;
+			input-enable;
+			silabs,input-filter;
+		};
+	};
+};
+
+dut: &usart0 {
+	dmas = <&dma0 DMA_REQSEL_USART0TXBL>,
+	       <&dma0 DMA_REQSEL_USART0RXDATAV>;
+	dma-names = "tx", "rx";
+	pinctrl-0 = <&usart0_default>;
+	pinctrl-names = "default";
+};
+
+&usart1 {
+	current-speed = <115200>;
+	pinctrl-0 = <&usart1_default>;
+	pinctrl-names = "default";
+	status = "okay";
+};
+
+&dma0 {
+	status = "okay";
+};