stringlist-functions: add sorted insert ...

Add sorted insert in stringlist functions.
Also added function to checked if string is already
in string list.

Signed-off-by: Alexander Aring <a.aring@phytec.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

stringlist: Fix printing on smaller consoles ...

Do not add additional space between strings, we already
did this by adding 4 to the string length.

Signed-off-by: Sascha Hauer <sha@pengutronix.de>

add stringlist function. They can be used to build a list ...

of strings. For now mainly useful to print the resulting
list in columns which is used in tab completion and ls.