Introduction of libacpica to get pci irqs and shutdown

[Damien Zammit]

Hi!

This patch series has been tested to boot a rumpdisk
and fetch the PCI IRQs of disk controllers from acpi.static translator
via bootstrapping acpi -> pci -> rumpdisk -> ext2fs -> exec.

It also cleanly shuts down the machine by sending an RPC to acpi
to call the new shutdown method inside libacpica.

This series will require libacpica to be included as a hurd build-dep.
Also, rumpkernel will then depend on hurd-dev to get the acpi.defs file.

Damien