introduce and use relaxed cpumask bitops

introduce and use relaxed cpumask bitops

Using atomic (LOCKed on x86) bitops for certain of the operations on
cpumask_t is overkill when the variables aren't concurrently accessible
(e.g. local function variables, or due to explicit locking). Introduce
alternatives using non-atomic bitops and use them where appropriate.

Note that this
- adds a volatile qualifier to cpumask_test_and_{clear,set}_cpu()
  (should have been there from the beginning, like is the case for
  cpumask_{clear,set}_cpu())
- replaces several cpumask_clear()+cpumask_set_cpu(, n) pairs by the
  simpler cpumask_copy(, cpumask_of(n)) (or just cpumask_of(n) if we
  can do without copying)

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: George Dunlap <george.dunlap@eu.citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>