bootloader: Make CONFIG_SB_IMAGE_BOOT_OFFSET user configurable

Allow setting custom value to the Kconfig option.

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

Author: de-nordic

subsys/bootloader/Kconfig

@@ -16,12 +16,14 @@ config SECURE_BOOT
 	  Set this option to enable the first stage bootloader which
 	  verifies the signature of the app.
 
+
 config SB_IMAGE_BOOT_OFFSET
-	hex
+	hex "Offset of executable code within firmware image"
 	depends on !PARTITION_MANAGER_ENABLED
 	default 0x800 if SOC_SERIES_NRF54L
 	default 0x200 if SOC_SERIES_NRF53 || SOC_SERIES_NRF91
 	default 0x200 if SOC_SERIES_NRF52
+	default 0
 	help
 	  Size of offset, from the beginning of storage partition, or __rom_start,
 	  where to application code begins. This is usually size of non-executable