From: Matthew Dobson <colpatch@us.ibm.com>

This patch defines a topology macro for ppc64, nr_cpus_node(node) which
returns the number of CPUs on 'node'.  This patch also adds code to compute
and store these values in an array for quick lookup.

Test compiled and booted by Andrew Theurer (habanero@us.ibm.com) on both
x440 and ppc64.