Pull up following revision(s) (requested by tsutsui in ticket #1327):
sys/arch/amd64/amd64/mainbus.c: revision 1.28 via patch
sys/arch/x86/x86/mp.c: revision 1.2 via patch
sys/arch/i386/i386/mainbus.c: revision 1.85 via patch
sys/arch/x86/x86/mpacpi.c: patch
sys/arch/x86/x86/mpbios.c patch
Apply fixes from jmcneill@ for PR port-i386/38729
(ACPI kernel booted under qemu cannot detect devices):
- make MP SCANPCI function for ACPI_SCANPCI and MPBIOS_SCANPCI
  return a number of attached PCI busses
- if no valid PCI busses are attached in the MP SCANPCI function,
  try to probe and attach pci0 at mainbus as well as kernels
  with no SCANPCI options
"Feel free to check it in" from jmcneill@.
Tested in pkgsrc qemu-0.9.1 (both i386 and x86_64) on NetBSD/i386.
Note original jmcneill's patch was posted on March:
http://mail-index.NetBSD.org/port-i386/2009/03/24/msg001281.html
and I also applied it to amd64:
http://mail-index.NetBSD.org/port-i386/2009/03/24/msg001283.html
but x86 MP attach functions have been reorganized by dyoung@ on April:
http://mail-index.NetBSD.org/source-changes/2009/04/17/msg219992.html
so I've modified the original patches to adapt the changes.
(mpacpi_scan_pci() and mpbios_scan_pci() have been merged into
common mp_pci_scan() in new arch/x86/x86/mp.c)
For netbsd-5 and netbsd-5-0 branches, the original patches should be
applied cleanly, and they have been tested by abs@ on a selection of
i386 boxes and in qemu.

(bouyer)