Fix bug on SRIOV ReservedBusNum when ARI enable.

Fix bug on SRIOV ReservedBusNum when ARI enable.

If a device which support both features SR-IOV/ARI  has multi
functions, which maybe support 8-255. After enable ARI forwarding in
the root port and ARI Capable Hierarchy in the SR-IOV PF0.
The device will support and expose multi functions(0-255) with ARI ID routing.
In next device loop in below for() code, actually it still be in the
same SR-IOV device, and just some PF which is over 8 or higher
one(n*8), PciAllocateBusNumber() will allocate bus
number(ReservedBusNum - TempReservedBusNum)) for this PF. if reset
TempReservedBusNum as 0 in this case,it will allocate wrong bus number
for this PF because TempReservedBusNum should be total previous PF's
reserved bus numbers.

code:
  for (Device = 0; Device <= PCI_MAX_DEVICE; Device++) {
    TempReservedBusNum = 0;
    for (Func = 0; Func <= PCI_MAX_FUNC; Func++) {
    //
    // Check to see whether a pci device is present
    //
    Status = PciDevicePresent (
                 PciRootBridgeIo,
                 &Pci,
                 StartBusNumber,
                 Device,
                 Func
                 );
    ...
    Status = PciAllocateBusNumber (PciDevice, *SubBusNumber,
    (UINT8)(PciDevice->ReservedBusNum - TempReservedBusNum), SubBusNumber);

The solution is add a new flag IsAriEnabled to help handle this case.
if ARI is enabled, then TempReservedBusNum will not be reset again
during all functions(1-255) scan with checking flag IsAriEnabled.

Signed-off-by: Foster Nong <foster.nong@intel.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>