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/dummy_m68k.c b/hw/dummy_m68k.c
index cb9b2eb..5718ab6 100644
--- a/hw/dummy_m68k.c
+++ b/hw/dummy_m68k.c
@@ -63,8 +63,15 @@
     env->pc = entry;
 }
 
-QEMUMachine dummy_m68k_machine = {
+static QEMUMachine dummy_m68k_machine = {
     .name = "dummy",
     .desc = "Dummy board",
     .init = dummy_m68k_init,
 };
+
+static void dummy_m68k_machine_init(void)
+{
+    qemu_register_machine(&dummy_m68k_machine);
+}
+
+machine_init(dummy_m68k_machine_init);