Change virDevicePCIAddress to virPCIDeviceAddress

Change virDevicePCIAddress to virPCIDeviceAddress

We had both and the only difference was that the latter also included
information about multifunction setting.  The problem with that was that
we couldn't use functions made for only one of the structs (e.g.
parsing).  To consolidate those two structs, use the one in virpci.h,
include that in domain_conf.h and add the multifunction member in it.

Signed-off-by: Martin Kletzander <mkletzan@redhat.com>