[nrf noup] zephyr: Add NRF54L configuration

Adds default Kconfig configuration that allows to build MCUboot
for NRF54L.
Currently this configuration turns off WDT and FPROTECT,
which is TODO to fix.

Signed-off-by: Dominik Ermel <dominik.ermel@nordicsemi.no>

boot/zephyr/boards/nrf54l15dk_nrf54l15_cpuapp.conf

@@ -0,0 +1,12 @@
+# Copyright (c) 2020 Nordic Semiconductor ASA
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+# Ensure that the qspi driver is disabled by default
+CONFIG_NORDIC_QSPI_NOR=n
+
+# TODO: below are not yet supported and need fixing
+CONFIG_NRF_RTC_TIMER=n
+CONFIG_FPROTECT=n
+CONFIG_BOOT_WATCHDOG_FEED=n
+CONFIG_MULTITHREADING=y