qga:/qga-win: adding a empty PCI address creation function

Refactoring code to avoid duplication of creating an empty PCI address code.

Signed-off-by: Kfir Manor <kfir@daynix.com>
Reviewed-by: Konstantin Kostiuk <kkostiuk@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Konstantin Kostiuk <kkostiuk@redhat.com>