KVM: s390: Introduce BCD Vector Instructions to the guest

We can directly forward the vector BCD instructions to the guest
if available and VX is requested by user space.

Please note that user space will have to take care of the final state
of the facility bit when migrating to older machines.

Signed-off-by: Guenther Hutzl <hutzl@linux.vnet.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>