apic: Document why cannot_instantiate_with_device_add_yet

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Andreas Färber <afaerber@suse.de>

hw/intc/apic_common.c

@@ -386,9 +386,13 @@ static void apic_common_class_init(ObjectClass *klass, void *data)
 
     dc->vmsd = &vmstate_apic_common;
     dc->reset = apic_reset_common;
-    dc->cannot_instantiate_with_device_add_yet = true; /* FIXME explain why */
     dc->props = apic_properties_common;
     idc->init = apic_init_common;
+    /*
+     * Reason: APIC and CPU need to be wired up by
+     * x86_cpu_apic_create()
+     */
+    dc->cannot_instantiate_with_device_add_yet = true;
 }
 
 static const TypeInfo apic_common_type = {