kern: Implement all dead and no prefixed functions in kern_conf

[aokblast]

Summary

This prevents KCFI to fail

[imp]

C had finally outpaced the generic catch-all function... eopnotsupp, or similar, has been around since at least v4 (the first C version we have).

nodev()
{
        u.u_error = ENODEV;
}

I know this is for one of the kernel sanitizers and not strictly forced by new C behavior, but still...