tests: drivers: uart: add uart_async_api support for frdm_mcxa156 board

add uart_async_api test support for frdm_mcxa156 board

Signed-off-by: Neil Chen <[email protected]>

Author: NeilChen93

tests/drivers/uart/uart_async_api/boards/frdm_mcxa156.overlay

@@ -0,0 +1,9 @@
+/*
+ * Copyright 2024 NXP
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/*
+ * To test this sample connect P3_20 to P3_21
+ */
+dut: &lpuart1 {};