Integrate meta-seconorth-machine/add_6ull_bootwdog

Commit: seco-ne/yocto/layers/meta-seconorth-machine@1b755691

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