tests: drivers: uart: Add support for uart_async_api on mck_ra8t2

Add support for test app "uart_async_api" on Renesas mck_ra8t2

Signed-off-by: Khoa Tran <[email protected]>

Author: khoatranyj

tests/drivers/uart/uart_async_api/boards/mck_ra8t2_r7ka8t2lfecac_cm85.overlay

@@ -0,0 +1,10 @@
+/*
+ * Copyright (c) 2025 Renesas Electronics Corporation
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+&sci4 {
+	dut: uart {
+		status = "okay";
+	};
+};