[PATCH] x86_64: fls in asm for x86_64

Use single instruction for find largest set bit on x86_64.

[Updated by Jan Beulich to fix wrong asm constraints in original
patch -AK]

Cc: jbeulich@novell.com
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>