s390x: Return specification exception for unimplemented diag 308 subcodes

The architecture specifies specification exceptions for all
unavailable subcodes.

The presence of subcodes is indicated by checking some query subcode.
For example 6 will indicate that 3-6 are available. So future systems
might call new subcodes to check for new features. This should not
trigger a hw error, instead we return the architectured specification
exception.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Cc: qemu-stable@nongnu.org
Message-Id: <20190111113657.66195-3-frankja@linux.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>

target/s390x/diag.c

@@ -130,7 +130,7 @@ out:
         }
         return;
     default:
-        hw_error("Unhandled diag308 subcode %" PRIx64, subcode);
+        s390_program_interrupt(env, PGM_SPECIFICATION, ILEN_AUTO, ra);
         break;
     }
 }