[PATCH] x86_64: Clean up copy_*_user

- Remove optimization for old B stepping Opteron
- Make the fast path for copies with a multiple of eight length faster.
- Minor instruction rearrangement to hopefully avoid a pipeline
stall or two.
- Add comment about errata to consider.

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>