pci: helper functions to access PCIDevice::config add helper functions to get/set PCIDevice::config Those will be used later. Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp> Acked-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>