x86/PCI: Ignore _SEG on HP xw9300

The xw9300 BIOS supplies _SEG methods that are incorrect, which results
in some LSI SCSI devices not being discovered.  This adds a quirk to
ignore _SEG on this machine and default to zero.

The xw9300 has three host bridges:

    ACPI: PCI Root Bridge [PCI0] (domain 0000 [bus 00-3f])
    ACPI: PCI Root Bridge [PCI1] (domain 0001 [bus 40-7f])
    ACPI: PCI Root Bridge [PCI2] (domain 0002 [bus 80-ff])

When the BIOS "ACPI Bus Segmentation" option is enabled (as it is by
default), the _SEG methods of the PCI1 and PCI2 bridges return 1 and 2,
respectively.  However, the BIOS implementation appears to be incomplete,
and we can't enumerate devices in those domains.

But if we assume PCI1 and PCI2 really lead to buses in domain 0,
everything works fine.  Windows XP and Vista also seem to ignore
these _SEG methods.

Reference: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=543308
Reference: https://bugzilla.kernel.org/show_bug.cgi?id=15362
Reported-and-Tested-by: Sean M. Pappalardo <pegasus@renegadetech.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

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