samples/dfu/fw_loader/usb_mcumgr: nRF54lm20dongle configuration

Added peculiar configuration for the nrf54lm20dongle/nrf54lm20b/cpuapp
It has only to build sucessfully as this sample is supposed to be use
as part of a DFU multiimage sysbuild project.

Signed-off-by: Andrzej Puzdrowski <andrzej.puzdrowski@nordicsemi.no>

Author: nvlsianpu

samples/dfu/fw_loader/usb_mcumgr/boards/nrf54lm20dongle_nrf54lm20b_cpuapp.overlay

@@ -0,0 +1,21 @@
+/*
+ * Copyright (c) 2026 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
+ */
+
+/ {
+	chosen {
+		/delete-property/ zephyr,console;
+		/delete-property/ zephyr,shell-uart;
+		/delete-property/ zephyr,bt-mon-uart;
+		/delete-property/ zephyr,bt-c2h-uart;
+		zephyr,uart-mcumgr = &cdc_acm_uart0;
+	};
+};
+
+&zephyr_udc0 {
+	/delete-node/ board_cdc_acm_uart;
+};
+
+#include "../app.overlay"

samples/dfu/fw_loader/usb_mcumgr/sample.yaml

@@ -9,5 +9,7 @@ tests:
       - ci_samples_dfu
     platform_allow:
       - nrf54lm20dk/nrf54lm20a/cpuapp
+      - nrf54lm20dongle/nrf54lm20b/cpuapp
     integration_platforms:
       - nrf54lm20dk/nrf54lm20a/cpuapp
+      - nrf54lm20dongle/nrf54lm20b/cpuapp