scripts: kconfig: Import Kconfiglib

Import Kconfiglib, the Python Kconfig parsing library.

Origin: https://github.com/ulfalizer/Kconfiglib


Revision: 8d30e5bb1ad5cab16d1226cc5cd3a03d64664f5d

Note that this will in time replace doc/scripts/genrest/kconfiglib.py,
which is an earlier version and should not live in that folder.

Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>