Fix linking to DTrace probes file

Fix linking to DTrace probes file

There was no rule forcing libvirt_qemu_probes.o to be built
before libvirt_qemu_probes.lo was used. Also libvirtd was
still referencing the .o file, rather than the .lo file.

Both the .lo and .o file must be listed as DEPENDENCIES,
otherwise libtool will unhelpfully delete the .o file
once the .lo file is created.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>