x86: allow machine_crash_shutdown to be replaced

This patch a llows machine_crash_shutdown to
be replaced, just like any of the other functions
in machine_ops

Signed-off-by: Glauber Costa <gcosta@redhat.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
diff --git a/include/asm-x86/reboot.h b/include/asm-x86/reboot.h
index 6b5233b..0891a41 100644
--- a/include/asm-x86/reboot.h
+++ b/include/asm-x86/reboot.h
@@ -15,5 +15,6 @@
 extern struct machine_ops machine_ops;
 
 void machine_real_restart(unsigned char *code, int length);
+void native_machine_crash_shutdown(struct pt_regs *regs);
 
 #endif	/* _ASM_REBOOT_H */