Xen: use proper device ID to search VT-d unit for ARI and SR-IOV device

Xen: use proper device ID to search VT-d unit for ARI and SR-IOV device

PCIe Alternative Routing-ID Interpretation (ARI) ECN defines the Extended
Function -- a function whose function number is greater than 7 within an
ARI Device. Intel VT-d spec 1.2 section 8.3.2 specifies that the Extended
Function is under the scope of the same remapping unit as the traditional
function. The hypervisor needs to know if a function is Extended
Function so it can find proper DMAR for it.

And section 8.3.3 specifies that the SR-IOV Virtual Function is under the
scope of the same remapping unit as the Physical Function. The hypervisor
also needs to know if a function is the Virtual Function and which
Physical Function it's associated with for same reason.

Signed-off-by: Yu Zhao <yu.zhao@intel.com>