sys/i386/xen_mp_machdep.c:
	Set a 'fake' acpi_id for the i386 PV port, it is needed in
	order to use VIRQs or IPI event channels.

Submitted by:	Roger Pau Monné
Sponsored by:	Citrix Systems R&D
Reviewed by:	gibbs
Approved by:	re (blanket Xen)
MFC after:	2 weeks