xen, gfx passthrough: register host bridge specific to passthrough Just register that pci host bridge specific to passthrough. Signed-off-by: Tiejun Chen <tiejun.chen@intel.com> Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com> Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>