x86: not set boot cpu in cpu_present_map again

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

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>