x86: make native_machine_shutdown non-static

it will allow external users to call it. It is mainly
useful for routines that will override its machine_ops
field for its own special purposes, but want to call the
normal shutdown routine after they're done

Signed-off-by: Glauber Costa <gcosta@redhat.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index 0f1d567..a4a8383 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -399,7 +399,7 @@
 	}
 }
 
-static void native_machine_shutdown(void)
+void native_machine_shutdown(void)
 {
 	/* Stop the cpus and apics */
 #ifdef CONFIG_SMP