Merge branch 'tglx-license' into docs-next

Thomas said:

There are a few bogus SPDX identifiers in various files and SPDX
Identifiers used in tree or about to be used which have no corresponding
License Text file in the LICENSES directory or use the new variant of the
GPL-2.0[+] license identifiers which are not mentioned in the GPL-2.0
Valid-License-Identifiers: tags.

There is no tool which can be used to scan the tree and also nothing which
helps people who submit patches to check their stuff before submission.

The following series cleans that up:

 - Add GPL-2.0-only and GPL-2.0-or-later identifiers to the GPL2.0 license
   and the Linux-syscall-note exception

 - Add X11, Apache-2.0, CC-BY-SA-4.0, CCDL-1.0, Linux-OpenIB license texts
   to the LICENSES directory along with the required documentation texts

 - Add a checker script which can read a single file or even a patch from
   the command line or does a full git tree scan

[Thomas also wins some sort of special prize for including an SPDX-checking
patch that complains about itself!]