Pull up following revision(s) (requested by chs in ticket #683):
sys/arch/ia64/include/acpi_machdep.h: revision 1.6
sys/arch/x86/include/acpi_machdep.h: revision 1.11
sys/dev/acpi/acpi.c: revision 1.255
sys/arch/x86/acpi/acpi_machdep.c: revision 1.4
sys/arch/x86/x86/mpacpi.c: revision 1.95
sys/arch/x86/x86/mpacpi.c: revision 1.96
sys/arch/ia64/acpi/acpi_machdep.c: revision 1.6
locate PCI buses and determine their bus numbers using the info
previously extracted from ACPICA rather than trying to figure it out again.
allow PCI buses that don't have a _PRT method.
as a workaround for PR 47016, call ioapic_reenable() at the end of
ACPI interrupt routing to fix the settings for the SCI interrupt.
the problem is that after my recent changes, the SCI handler is
installed before the MADT info is parsed, so we don't know what
polarity it should have.  the real fix for this will be to rearrange
the ACPI initialization so that everything is done in a more sensible
order, but that will take some more time.

(riz)