x86: call machine_shutdown and stop all CPUs in native_machine_halt

Impact: really halt all CPUs on halt

Function machine_halt (resp. native_machine_halt) is empty for x86
architectures. When command 'halt -f' is invoked, the message "System
halted." is displayed but this is not really true because all CPUs are
still running.

There are also similar inconsistencies for other arches (some uses
power-off for halt or forever-loop with IRQs enabled/disabled).

IMO there should be used the same approach for all architectures OR
what does the message "System halted" really mean?

This patch fixes it for x86.

Signed-off-by: Ivan Vecera <ivecera@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/reboot.c

@@ -461,6 +461,11 @@ static void native_machine_restart(char *__unused)
 
 static void native_machine_halt(void)
 {
+	/* stop other cpus and apics */
+	machine_shutdown();
+
+	/* stop this cpu */
+	stop_this_cpu(NULL);
 }
 
 static void native_machine_power_off(void)