From: Matthew Dobson <colpatch@us.ibm.com>

The code to parse the EBDA (Extended BIOS Data Area) for Summit boxen is
broken because it does not handle Lookout boxen (external boxes full of
additional PCI slots).  This patch cleans up some ugliness in
arch/i386/kernel/summit.c as well as fixing the code to handle Lookout boxen
and various other configurations of PCI buses.  Without this, Summit PCI bus
to node mappings are totally hosed with Lookout boxen attatched.  This patch
depends upon the GENERICARCH fix.