qemu: fix CPU model error probing capabilities for ppc
qemu: fix CPU model error probing capabilities for ppc

The CPU driver only supports CPU models for PPC64 architecture, not
plain PPC.

  Failed to probe capabilities for /usr/bin/qemu-system-ppc:
  this function is not supported by the connection driver:
  'ppc' architecture is not supported by CPU driver

This fixes a bug in

  commit db873ab3bc5f6fbd7d227727a62ccfee3d1c3e9d
  Author: Jiri Denemark <jdenemar@redhat.com>
  Date:   Thu May 17 17:08:42 2018 +0200

    qemu: Adapt to changed ppc64 CPU model names

Reviewed-by: Daniel Henrique Barboza <627b089ad62deae9aaf06ccfa2c9056df28927e0@gmail.com>
Reviewed-by: Andrea Bolognani <3ada0bee826c753786fdbba72243dfba997094cf@redhat.com>
Signed-off-by: Daniel P. Berrangé <bb938cf255e055ff3507f2627d214e8e62118fcf@redhat.com>

libvirt/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,libvirt/libvirt,crobinso/libvirt,nertpinx/libvirt,zippy2/libvirt,fabianfreyer/libvirt,jfehlig/libvirt,olafhering/libvirt,crobinso/libvirt,zippy2/libvirt,crobinso/libvirt,libvirt/libvirt,zippy2/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,olafhering/libvirt,crobinso/libvirt,nertpinx/libvirt,jfehlig/libvirt,jardasgit/libvirt,olafhering/libvirt,zippy2/libvirt,jardasgit/libvirt,libvirt/libvirt,jardasgit/libvirt,fabianfreyer/libvirt,jardasgit/libvirt,olafhering/libvirt,jardasgit/libvirt,jfehlig/libvirt,jfehlig/libvirt