Convert machine registration to use module init functions

This cleans up quite a lot of #ifdefs, extern variables, and other ugliness.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/hw/ppce500_mpc8544ds.c b/hw/ppce500_mpc8544ds.c
index b630315..632fb05 100644
--- a/hw/ppce500_mpc8544ds.c
+++ b/hw/ppce500_mpc8544ds.c
@@ -281,8 +281,15 @@
     return;
 }
 
-QEMUMachine mpc8544ds_machine = {
+static QEMUMachine mpc8544ds_machine = {
     .name = "mpc8544ds",
     .desc = "mpc8544ds",
     .init = mpc8544ds_init,
 };
+
+static void mpc8544ds_machine_init(void)
+{
+    qemu_register_machine(&mpc8544ds_machine);
+}
+
+machine_init(mpc8544ds_machine_init);