Add an notsc option so that it can be turned off again.

This may be useful on the Summit, but will only work when there is a HPET
fallback.
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>