[PATCH] x86_64: Some fixes for single step handling

Ported from i386/Linus

Be more careful with TF handling to fix some copy protection codes in Wine

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