Enable HVM guest VT-d device hotplug via a simple ACPI hotplug device model.

Enable HVM guest VT-d device hotplug via a simple ACPI hotplug device model.

Finish merge of remaining parts of xen-unstable c/s
17056:c6eeb71a85cffe917bc8d6738fd36e6694dba4d6:

    Enable HVM guest VT-d device hotplug via a simple ACPI hotplug device model.

    ** Currently only 2 virtual hotplug pci slots(6~7) are created so more
       than 2 vtd dev can't be hotplugged, but we can easily extend it in
       future.

    Three new commands are added:
    "xm pci-list domid" show the current assigned vtd device, like:
    VSlt  domain   bus   slot   func
    0x6      0x0  0x02   0x00    0x0

    "xm pci-detach" hot remove the specified vtd device by the virtual
    slot, like:
    xm pci-detach EdwinHVMDomainVtd 6

    "xm pci-attach DomainID dom bus dev func [vslot]" hot add a new vtd
    device in the vslot. If no vslot specified, a free slot will be picked
    up. e.g. to insert '0000:03:00.0':
    xm pci-attach EdwinHVMDomainVtd 0 3 0 0

    ** guest pci hotplug
    linux: pls. use 2.6.X and enable ACPI PCI hotplug ( Bus options=> PCI
    hotplug => ACPI PCI hotplug driver )
    windows: 2000/xp/2003/vista are all okay

    Signed-off-by: Zhai Edwin <edwin.zhai@intel.com>