[nrf fromtree] tests: drivers: uart: uart_async_api: Cleanup after nRF54LM20 rename

Remove duplicated test configuration after
nrf54l20pdk/nrf54l20/cpuxxx was renamed to
nrf54lm20dk/nrf54lm20a/cpuxxx.

Add test on fast instance uart00 on nrf54lm20dk.

Signed-off-by: Sebastian Głąb <[email protected]>
(cherry picked from commit e5a9c35)

Author: nordic-segl

tests/drivers/uart/uart_async_api/boards/nrf54l20pdk_nrf54l20_cpuapp.overlay

@@ -1,3 +1,9 @@
+/*
+ * Copyright (c) 2025 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
 /* Test requires following loopback:
  * P1.13 - P1.14
  */

tests/drivers/uart/uart_async_api/boards/nrf54lm20dk_nrf54lm20_common.dtsi

@@ -0,0 +1 @@
+CONFIG_VAR_LENGTH_BUFFER_TEST_BUADRATE_LIMIT=57600

tests/drivers/uart/uart_async_api/boards/nrf54lm20dk_nrf54lm20a_cpuapp.conf

@@ -0,0 +1,42 @@
+/*
+ * Copyright (c) 2025 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/* Test requires following loopback:
+ * P2.02 - P2.00
+ */
+
+&pinctrl {
+	uart00_default_alt: uart00_default_alt {
+		group1 {
+			psels = <NRF_PSEL(UART_TX, 2, 2)>;
+		};
+
+		group2 {
+			psels = <NRF_PSEL(UART_RX, 2, 0)>;
+			bias-pull-up;
+		};
+	};
+
+	uart00_sleep_alt: uart00_sleep_alt {
+		group1 {
+			psels = <NRF_PSEL(UART_TX, 2, 2)>,
+				<NRF_PSEL(UART_RX, 2, 0)>;
+			low-power-enable;
+		};
+	};
+};
+
+dut: &uart00 {
+	status = "okay";
+	pinctrl-0 = <&uart00_default_alt>;
+	pinctrl-1 = <&uart00_sleep_alt>;
+	pinctrl-names = "default", "sleep";
+	current-speed = <4000000>;
+};
+
+&gpio2 {
+	status = "okay";
+};

tests/drivers/uart/uart_async_api/boards/nrf54lm20dk_nrf54lm20a_cpuapp_uart00.overlay

@@ -18,6 +18,14 @@ tests:
       - platform:mimxrt685_evk/mimxrt685s/cm33:"DTC_OVERLAY_FILE=nxp/dut_flexcomm4.overlay"
       - platform:mimxrt595_evk/mimxrt595s/cm33:"DTC_OVERLAY_FILE=nxp/dut_flexcomm12.overlay"
       - platform:frdm_rw612/rw612:"DTC_OVERLAY_FILE=nxp/dut_lpc_flexcomm0.overlay"
+  drivers.uart.async_api.fast:
+    harness: ztest
+    harness_config:
+      fixture: uart_fast_loopback
+    platform_allow:
+      - nrf54lm20dk/nrf54lm20a/cpuapp
+    extra_args:
+      - DTC_OVERLAY_FILE="boards/nrf54lm20dk_nrf54lm20a_cpuapp_uart00.overlay"
   drivers.uart.wide:
     filter: CONFIG_SERIAL_SUPPORT_ASYNC and not CONFIG_UART_MCUX_LPUART
     harness: ztest