Adding LICENSES folder for REUSE

[Charlemagne Lasse]

Hi,

the linux kernel is a GPL-2.0 project but is build based on files using
all kinds of different licenses. It would be really nice when these
licenses could be correctly referenced as described in the
https://reuse.software/practices/ from the FSF.

Since some people started to add the SPDX headers to some files, it
might now be the right time to ask to get a LICENSES folder which will
contain the separate licenses. According to the currently existing
SPDX-License-Identifier, this should be at least:

- GPL-1.0
- GPL-2.0
- BSD-2-Clause
- BSD-3-Clause
- MIT
- MPL-1.1
- LGPL-2.0
- LGPL-2.1

I personally don't understand why BSD-2-Clause or MIT needs to have the
copyright file stored with the copyright holder while GPL-2.0 doesn't
need that. Seems to be quite wasteful and useless in a project like the
Linux kernel. Especially when there are multiple copyright holders - and
there are different combination in each file. Maybe the FSFE can give us
some insights here.

Here just two example files:

- https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/net/wireless/ath/ath9k/dfs.c?id=b39545684a90ef3374abc0969d64c7bc540d128d
- https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/net/wireless/ath/ath9k/ar9580_1p0_initvals.h?id=b39545684a90ef3374abc0969d64c7bc540d128d

It would also be interesting to know from the FSFE how dual license
should be handled in by the License-Filename tag.


Thanks,
Charlemagne Lasse