Only display physical id/siblings when there are siblings or dual core.

In 2.6.11 I accidentially broke it and it was always displaying these
fields But for compatibility to all these /proc parsers around it is better
to do it in the old way again.  

Noticed by Suresh Siddha

Cc: <Suresh.b.siddha@intel.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>