sched, mm, x86: Add the ARCH_SUPPORTS_NUMA_BALANCING flag

sched, mm, x86: Add the ARCH_SUPPORTS_NUMA_BALANCING flag

Allow architectures to opt-in to the adaptive affinity NUMA balancing code.

Cc: 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>