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

This patch implements a generic version of the nr_cpus_node(node) macro
implemented for ppc64 by the previous patch.

The generic version simply computes an hweight of the bitmask returned by
node_to_cpumask(node) topology macro.

This patch also adds a generic_hweight64() function and an hweight_long()
function which are used as helpers for the generic nr_cpus_node() macro.

This patch also adds a for_each_node_with_cpus() macro, which is used in
sched_best_cpu() in kernel/sched.c to fix the original problem of
scheduling processes on CPU-less nodes.  This macro should also be used in
the future to avoid similar problems.

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