update to u-root 0.12.0 and more cleanups

[majst01]

TODO:

depends on: metal-stack/go-hal#60

• use go-1.21
• switch to slog
• test
  • machine creation worked

[majst01]

[   12.422948] cgroup: Unknown subsys name 'net_cls'
[   12.427728] cgroup: Unknown subsys name 'hugetlb'
/bbin/uinit: errdefaultsh-5.1# uinit
uinit: error while loading shared libraries: libpcap.so.0.8: cannot open shared object file: No such file or directory
defaultsh-5.1#