x86: not set boot cpu in cpu_online_map in smp_prepare_boot_cpu()

in init/main.c boot_cpu_init() does that before.

Signed-off-by: Yinghai Lu <yinghai.lu@sun.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>