doc: hashdist defaults on for 64bit

kernel boot parameter `hashdist' now defaults on for all 64bit NUMA.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>