Don't use the I/O APIC by default,

since this would require pcid to know the _PRT (PCI routing table) to
use and map the interrupt pins to the correct IRQs. xhcid is unaffected
by this though, since it uses MSI-X.

All ACPI handling will be done in userspace before the infrastructure
necessary would make sense (I don't think adding serde to the kernel
would be optimal, and how else would all of the ACPI namespace be
parsed?).