lib: list_sort: delete dead code ...

list_sort.c's core code should only change on sync with Linux, so we
don't really need separate testing code. The code doesn't compile as
we neither have a CONFIG_TEST_LIST_SORT symbol nor do we have a
<linux/random.h> header. Remove it.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

recursive_action: add ACTION_SORT flag ...

Add a flag to sort directory entries before recursing into them.

Since this part of lib/ is used inside barebox as well as in
scripts/bareboxenv.c, we cannot easily use stringlists from lib/, which
would have made the code a bit nicer.

Signed-off-by: Florian Bäuerle <florian.baeuerle@allegion.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Add list_sort from u-boot v2016.03 ...

This is required by UBIFS update.

Signed-off-by: Alexander Stein <alexander.stein@systec-electronic.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>