hw: apply accel compat properties without touching globals

Instead of registering compat properties as globals, let's keep them
in their own array, to avoid mixing with user globals.

Introduce object_apply_global_props() function, to apply compatibility
properties from a GPtrArray.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Acked-by: Eduardo Habkost <ehabkost@redhat.com>

vl.c

@@ -2996,7 +2996,6 @@ static void user_register_global_props(void)
  */
 static void register_global_properties(MachineState *ms)
 {
-    accel_register_compat_props(ms->accelerator);
     machine_register_compat_props(ms);
     user_register_global_props();
 }