Add a CPU_DOWN_PREPARE hotplug CPU notifier.  This is needed so we can dettach
all sched-domains before a CPU goes down, thus we can build domains from
online cpumasks, and not have to check for the possibility of a CPU coming up
or going down.
Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>