tests: Re-enable ppc64 cpu tests

Now that all the changes have been implemented we can run the
test cases once again, after updating them to reflect the new
behaviour.

tests/cputestdata/ppc64-host.xml

@@ -1,6 +1,6 @@
 <cpu>
   <arch>ppc64</arch>
-  <model>POWER7_v2.3</model>
+  <model>POWER7</model>
   <vendor>IBM</vendor>
   <topology sockets='1' cores='64' threads='1'/>
 </cpu>