qemu: Extended qemuDomainAssignAddresses to be callable from everywhere.

qemu: Extended qemuDomainAssignAddresses to be callable from everywhere.

This is in preparation of the enablement of s390 guests with virtio devices.

The assignment of device addresses happens in different places, i.e. the
qemu driver and process modules as well as in the unit tests in slightly
different flavors. Currently, these are PPC spapr-vio and PCI
devices, virtio-s390 (not PCI based) will follow.

By optionally passing to qemuDomainAssignAddresses the domain
object and the capabilities it is now possible to call the function
from most of the places (except for hotplug) where address assignment
is done.

Signed-off-by: Viktor Mihajlovski <mihajlov@linux.vnet.ibm.com>