[PATCH] xtensa: add asm/futex.h

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Chris Zankel <chris@zankel.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>