cpumask: switch over to cpu_online/possible/active/present_mask: core

Impact: cleanup

This implements the obsolescent cpu_online_map in terms of
cpu_online_mask, rather than the other way around.  Same for the other
maps.

The documentation comments are also updated to refer to _mask rather
than _map.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Mike Travis <travis@sgi.com>