Remove unneeded ifdef in hardirq.h

I can't see any reason for the #ifdef CONFIG_X86 introduced to the x86_64
hardirq.h as part of the generic irq subsystem changes.
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>