Introduce pci-serial
    
    https://bugzilla.redhat.com/show_bug.cgi?id=998813
    
    Like usb-serial, the pci-serial device allows a serial device to be
    attached to PCI bus. An example XML looks like this:
    
      <serial type='dev'>
        <source path='/dev/ttyS2'/>
        <target type='pci-serial' port='0'/>
        <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
      </serial>
    
    Signed-off-by: Michal Privoznik <mprivozn@redhat.com>