virtio-pci: refactor virtio-pci device. Create the virtio-pci device which is abstract. This transport device will create a virtio-pci-bus, so one VirtIODevice can be connected. Signed-off-by: KONRAD Frederic <fred.konrad@greensocs.com> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>