s390: Cpu driver support for update and compare

s390: Cpu driver support for update and compare

Implement compare for s390. Required to test the guest against the host for
guest cpu model runnability checking. We always return IDENTICAL to bypass
Libvirt's checking. s390 will rely on Qemu to perform the runnability checking.

Implement update for s390. required to support use of cpu "host-model" mode.

Signed-off-by: Jason J. Herne <jjherne@linux.vnet.ibm.com>
Acked-by: Jiri Denemark <jdenemar@redhat.com>