Add ktrace, profcs & hwpmc to FreeBSD section

Notes from sys/kern/kern_prot.c:

```
/*
 * The 'unprivileged_proc_debug' flag may be used to disable a variety of
 * unprivileged inter-process debugging services, including some procfs
 * functionality, ptrace(), and ktrace().  In the past, inter-process
 * debugging has been involved in a variety of security problems, and sites
 * not requiring the service might choose to disable it when hardening
 * systems.
```

See Also:

 * hwpmc(4)
 * p_candebug(9)