PCI: fix pci_bus_alloc_resource() hang, prefer positive decode

When a PCI bus has two resources with the same start/end, e.g.,

    pci_bus 0000:04: resource 2 [mem 0xd0000000-0xd7ffffff pref]
    pci_bus 0000:04: resource 7 [mem 0xd0000000-0xd7ffffff]

the previous pci_bus_find_resource_prev() implementation would alternate
between them forever:

    pci_bus_find_resource_prev(... [mem 0xd0000000-0xd7ffffff pref])
        returns [mem 0xd0000000-0xd7ffffff]
    pci_bus_find_resource_prev(... [mem 0xd0000000-0xd7ffffff])
        returns [mem 0xd0000000-0xd7ffffff pref]
    pci_bus_find_resource_prev(... [mem 0xd0000000-0xd7ffffff pref])
        returns [mem 0xd0000000-0xd7ffffff]
    ...

This happened because there was no ordering between two resources with the
same start and end.  A resource that had the same start and end as the
cursor, but was not itself the cursor, was considered to be before the
cursor.

This patch fixes the hang by making a fixed ordering between any two
resources.

In addition, it...