kboot: update copyright on these files.

host_syscalls.c: I've written, so put Netflix copyright on. It's
possible in the confusion that Nathan wrote the host_gettimeofday
implementation.

syscall_nr: These files likely can't enjoy copyright protection since
they are just facts (the per-arch Linux system calls), so add a note
they are in the public domain.

Sponsored by: Netflix

kboot: Move system calls to libkboot

Sponsored by: Netflix