Add x86_64 support for Jack Steiner's SLIT sysfs patch

Make Jack's code compile on x86-64 and add x86-64 low level support to save
the SLIT pointer and a node_distance() implementation.

Requires the previous SRAT patch.
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>