i386: no need to make enable_cpu_hotplug a variable

As long as there's no write access to this variable there's no reason to
let gcc check it at runtime.

[ tglx: arch/x86 adaptation ]

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>