S390: Bail out without KVM

Currently only the S390 KVM target works. To keep users from accidently not
using KVM, let's not even initialize the machine when KVM is not used.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

hw/s390-virtio.c

@@ -142,6 +142,13 @@ static void s390_init(ram_addr_t ram_size,
     ram_addr_t initrd_size = 0;
     int i;
 
+    /* XXX we only work on KVM for now */
+
+    if (!kvm_enabled()) {
+        fprintf(stderr, "The S390 target only works with KVM enabled\n");
+        exit(1);
+    }
+
     /* get a BUS */
     s390_bus = s390_virtio_bus_init(&ram_size);