rather than finding our parent pcib and using its PCI_READ_CONFIG
method.
- Fix the defines for the 32-bit I/O decode registers, and properly
process the 16-bit versions. Now we will correctly check that I/O
resources behind the bridge are going to be decoded.
- Bring the quirk for the Orion PCI:PCI bridge in here (since it
seems to want to set the secondary/supplementary bus numbers).
- Use PCI_SLOTMAX rather than a magic number.