x86/xor: Add alternative SSE implementation only prefetching once per 64-byte line

On CPUs with 64-byte last level cache lines, this yields roughly
10% better performance, independent of CPU vendor or specific
model (as far as I was able to test).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/5093E4B802000078000A615E@nat28.tlf.novell.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>