[PATCH] powerpc: don't add memory to empty node/zone

The system will oops if an attempt is made to add memory to an
empty node/zone.  This patch prevents adding memory to an empty
node.  The code to dynamically add a node/zone is non-trivial.
This patch is temporary and will be removed when the ability
to dynamically add a node/zone is complete.

Signed-off-by: Mike Kravetz <kravetz@us.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>