LICENSING: clarify licenses of imported / reused code

The Zephyr kernel tree has imported or reuses packages, scripts that
are not covered by the Apache LICENSE.

As in some places it is not clear (there is no LICENSE file or way to
put it there), here we list them to ensure there is proper license
acknowledgement.

This is an initial proposal--I welcome feedback on everything,
especially where to link the documentation (kind of kludgy now) and
more missed components from this initial list.

v5: Added David Kinder's feedback

v4: Fixed more typos in Makefile

v3: fixed some more typos, but still holding on to feedback on how it
can be done with SPDX files, as it is not yet all clear to me.

Jira: ZEP-1079
Change-Id: Ie1bf545e26b0d304cd3ea0d70cdfc13d520197fe
Signed-off-by: Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>