Integrate meta-guf-machine/add-kernel-devicetrees-to-image-boot-files

Commit: https://gitlab.com/garz-fricke/yocto/layers/meta-guf-machine/-/commit/b86fb4ed3dbb97b886684103493f84bb64a40077

machine:guf: Automatically add devicetree to IMAGE_BOOT_FILES

We had separate lists, but all files in KERNEL_DEVICETREE are IMAGE_BOOT_FILES. So this can be replaced by an expression.