add MX6ULL specific boot-script with watchdog
Due to sporadic issues with Dunfell kernel 5.10 on NALLINO (occasionally initialization of display-controller hangs due to (seemingly) display clock not working) we add a boot watch-dog in the OS bootscript for 6ULL
Details see: https://projekte/bcs/ticketdetail/main/display?oid=1656043048275_JAnnotation