[nrf noup] zephyr: Get RWX skip size from ROM offset

Use CONFIG_ROM_START_OFFSET to set
CONFIG_NCS_MCUBOOT_DISABLE_SELF_RWX_SKIP_SIZE, instead of hardcoding
it for nRF54L.

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

Author: de-nordic

boot/zephyr/Kconfig

@@ -557,7 +557,7 @@ config NCS_MCUBOOT_DISABLE_SELF_RWX_SKIP_SIZE
 	hex
 	depends on NCS_MCUBOOT_DISABLE_SELF_RWX
 	depends on !PARTITION_MANAGER_ENABLED
-	default 0x800 if SOC_SERIES_NRF54L
+	default ROM_START_OFFSET if SOC_SERIES_NRF54L
 	help
 	  Size of region, at the beginning of the partition, that does not require
 	  protections. This is used, for example, when MCUboot type image is protected