sched, numa, mm, arch: Add variable locality exception

sched, numa, mm, arch: Add variable locality exception

Some architectures (ab)use NUMA to represent different memory
regions all cpu-local but of different latencies, such as SuperH.

The naming comes from Mel Gorman.

Named-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>