iommu/vt-d: Don't reject NTB devices due to scope mismatch

On a system with an Intel PCIe port configured as an NTB device, iommu
initialization fails with

    DMAR: Device scope type does not match for 0000:80:03.0

This is because the DMAR table reports this device as having scope 2
(ACPI_DMAR_SCOPE_TYPE_BRIDGE):

    [0A0h 0160   1]      Device Scope Entry Type : 02
    [0A1h 0161   1]                 Entry Length : 08
    [0A2h 0162   2]                     Reserved : 0000
    [0A4h 0164   1]               Enumeration ID : 00
    [0A5h 0165   1]               PCI Bus Number : 80

    [0A6h 0166   2]                     PCI Path : 03,00

but the device has a type 0 PCI header:

    80:03.0 Bridge [0680]: Intel Corporation Device [8086:2f0d] (rev 02)
    00: 86 80 0d 2f 00 00 10 00 02 00 80 06 10 00 80 00
    10: 0c 00 c0 00 c0 38 00 00 0c 00 00 00 80 38 00 00
    20: 00 00 00 c8 00 00 10 c8 00 00 00 00 86 80 00 00
    30: 00 00 00 00 60 00 00 00 00 00 00 00 ff 01 00 00

VT-d works perfectly on this system, so there's no reason to bail out
on initialization due to this apparent scope mismatch.  Use the class
0x0680 ("Other bridge device") as a heuristic for allowing DMAR
initialization for non-bridge PCI devices listed with scope bridge.

Signed-off-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>