pseries: Add 2.8 machine type, set up compatibility macros

Now that 2.7 is released, create the pseries-2.8 machine type and add the
boilerplate compatiblity macro stuff.  There's nothing new to put into the
2.7 compatiliby properties yet, but we'll need something eventually, so
we might as well get it ready now.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

hw/ppc/spapr.c

@@ -2436,19 +2436,37 @@ static const TypeInfo spapr_machine_info = {
     }                                                                \
     type_init(spapr_machine_register_##suffix)
 
+/*
+ * pseries-2.8
+ */
+static void spapr_machine_2_8_instance_options(MachineState *machine)
+{
+}
+
+static void spapr_machine_2_8_class_options(MachineClass *mc)
+{
+    /* Defaults for the latest behaviour inherited from the base class */
+}
+
+DEFINE_SPAPR_MACHINE(2_8, "2.8", true);
+
 /*
  * pseries-2.7
  */
+#define SPAPR_COMPAT_2_7 \
+    HW_COMPAT_2_7 \
+
 static void spapr_machine_2_7_instance_options(MachineState *machine)
 {
 }
 
 static void spapr_machine_2_7_class_options(MachineClass *mc)
 {
-    /* Defaults for the latest behaviour inherited from the base class */
+    spapr_machine_2_8_class_options(mc);
+    SET_MACHINE_COMPAT(mc, SPAPR_COMPAT_2_7);
 }
 
-DEFINE_SPAPR_MACHINE(2_7, "2.7", true);
+DEFINE_SPAPR_MACHINE(2_7, "2.7", false);
 
 /*
  * pseries-2.6