lib, list_sort: add list_sort from linux 3.14

from linux 3.14:

commit 455c6fdbd219161bd09b1165f11699d6d73de11c
Author: Linus Torvalds <torvalds@linux-foundation.org>
Date:   Sun Mar 30 20:40:15 2014 -0700

    Linux 3.14

Needed for the MTD/UBI/UBIFS resync

Just copied the files from Linux, and added in the c-file
the "#define __UBOOT__" for adding U-Boot special code. In
this case we use this just for adding including U-Boot
headers.

Signed-off-by: Heiko Schocher <hs@denx.de>
Cc: Marek Vasut <marex@denx.de>
Cc: Sergey Lapin <slapin@ossfans.org>
Cc: Scott Wood <scottwood@freescale.com>
Cc: Tom Rini <trini@ti.com>