KVM: s390: instruction-execution-protection support

The new Instruction Execution Protection needs to be enabled before
the guest can use it. Therefore we pass the IEP facility bit to the
guest and enable IEP interpretation.

Signed-off-by: Janosch Frank <frankja@linux.vnet.ibm.com>
Reviewed-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>