Impact: New APIs

The old node_to_cpumask/node_to_pcibus returned a cpumask_t: these
return a pointer to a struct cpumask.  Part of removing cpumasks from
the stack.

We can also use the new for_each_cpu_and() to avoid a temporary cpumask,
and a gratuitous test in sn_topology_show.

(Includes fix from KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>)
Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>
Cc: Tony Luck <tony.luck@intel.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>