cpumask: Use accessors for cpu_*_mask: sh

Use the accessors rather than frobbing bits directly (the new versions
are const).

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Mike Travis <travis@sgi.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>