Our (ab)use of cpu_possible_map in setup_system to start secondary SMT
threads bothers me.  Mark such threads in cpu_possible_map during early
boot; let RTAS tell us which present cpus are still offline later so we can
start them.

I'm not totally sure about this one, it might be better to set up
cpu_sibling_map in prom_hold_cpus and use that in setup_system.
Signed-off-by: Nathan Lynch <nathanl@austin.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>