qemu: extract PCI handling structs
    
    Introduce new files (domain_addr.[ch]) to provide
    an API for domain device handling that could be
    shared across the drivers.
    
    A list of data types were extracted and moved there:
    
     qemuDomainPCIAddressBus -> virDomainPCIAddressBus
     qemuDomainPCIAddressBusPtr -> virDomainPCIAddressBusPtr
     _qemuDomainPCIAddressSet -> virDomainPCIAddressSet
     qemuDomainPCIAddressSetPtr -> virDomainPCIAddressSetPtr
     qemuDomainPCIConnectFlags -> virDomainPCIConnectFlags
    
    Also, move the related definitions and macros.