move out pci internal structures, PCIBus, PCIBridge and pci_bus_info into
private header file, pci_internals.h.
This is a preparation. Later pci bridge implementation will be
split out form pci.c into pci_bridge.c.
Signed-off-by: NIsaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>