Hack to disable clustered mode on AMD systems

Make sure AMD big flat apic mode is not confused with clustered APIC 
mode. Ugly hack, but no better way found.
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>