dts: arm: add uart-mcumgr choosen for 54L15

setting uart20 as default uart-mcumgr

Signed-off-by: Mateusz Michalek <[email protected]>

Author: michalek-no

boards/nordic/nrf54l15pdk/nrf54l15pdk_nrf54l15_cpuapp.dts

@@ -16,6 +16,7 @@
 	chosen {
 		zephyr,console = &uart20;
 		zephyr,shell-uart = &uart20;
+		zephyr,uart-mcumgr = &uart20;
 		zephyr,sram = &sram0;
 		zephyr,flash = &rram0;
 		zephyr,code-partition = &slot0_partition;