KVM: s390: Support Configuration z/Architecture Mode

kvm has always supported the concept of starting in z/Arch mode so let's
reflect the feature bit to the guest.

Also, we change sigp set architecture to reject any request to change
architecture modes.

Signed-off-by: Jason J. Herne <jjherne@linux.vnet.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

arch/s390/tools/gen_facilities.c

@@ -80,6 +80,7 @@ static struct facility_def facility_defs[] = {
 			78, /* enhanced-DAT 2 */
 			130, /* instruction-execution-protection */
 			131, /* enhanced-SOP 2 and side-effect */
+			138, /* configuration z/architecture mode (czam) */
 			146, /* msa extension 8 */
 			-1  /* END */
 		}