The only change between the 2 linker scripts is the ORIGIN address of the flash memory allocated to InfiniTime. The MCUBoot one starts at 0x8000, which is the address that will be loaded by MCUBoot after the boot process. This linker script allow to run the application without MCUBoot by setting the origin address to 0x00. The APP_SIZE is the same for both linker scripts, but it could be set to a higher value in this one for development purposes.