Restructure VT-d device scope and PCI bridge handling

Restructure VT-d device scope and PCI bridge handling

Create a bitmap for each device scope indicating which buses are
covered by the scope.  Upon mapping PCI-PCI bridges we now detect
whether we have a bridge to a non-PCIe bus.  If so, all devices mapped
on that bus are squashed to the requester-id of the bridge.  Bridges
to PCIe busses are ignored.  The requester-id squashing also
determines the iommu device group id for the device.

Signed-off-by: Espen Skoglund <espen.skoglund@netronome.com>