Suggested by Ingo Molnar.

Drop APIC level workaround for old IO-APICs on x86-64 because it is a
significant part of interrupt handling time.  x86-64 only runs on modern
chipsets that probably don't have this bug.
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>