spapr: Use default_machine_opts to set suppress_vmdesc

Instead of setting suppress_vmdesc at instance_init time, set
default_machine_opts on spapr_machine_2_2_class_options() to
implement equivalent behavior.

This will let us eliminate the need for separate instance_init
functions for each spapr machine-type.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20181205205827.19387-4-ehabkost@redhat.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

hw/ppc/spapr.c

@@ -4368,13 +4368,13 @@ DEFINE_SPAPR_MACHINE(2_3, "2.3", false);
 static void spapr_machine_2_2_instance_options(MachineState *machine)
 {
     spapr_machine_2_3_instance_options(machine);
-    machine->suppress_vmdesc = true;
 }
 
 static void spapr_machine_2_2_class_options(MachineClass *mc)
 {
     spapr_machine_2_3_class_options(mc);
     SET_MACHINE_COMPAT(mc, SPAPR_COMPAT_2_2);
+    mc->default_machine_opts = "modern-hotplug-events=off,suppress-vmdesc=on";
 }
 DEFINE_SPAPR_MACHINE(2_2, "2.2", false);