Currently, there are some things that need to be set up by userspace
that the kernel previously did. These include telling firmware when the
I/O APIC is used, and most importantly, shutting down the system.

The former is not particularly important, but for the latter I think
that we could implement this using a "shutdown pipe". Essentially it
will be a file that triggers an event shutting down, which would be used
to notify to acpid that the kernel is requesting a shutdown.