WHENCE: extract license texts

WHENCE: extract license texts

Start extracting license texts from WHENCE into separate LICENSE files.

There are several reasons to do this:

1) Long license texts in the WHENCE are distracting and make parsing the
file more complicated.
2) Some licenses state that the terms must accompany the firmware when
redistributed, which is neater when the licence text is isolated instead
of having to use the entire contents of WHENCE.

Signed-off-by: Ross Burton <ross.burton@arm.com>