LICENSES: Add the BSD-3-clause "Clear" license

Add the full text of the BSD 3-clause "Clear" License to the
kernel tree.  It was copied directly from:

  https://spdx.org/licenses/BSD-3-Clause-Clear.html



Add the required tags for reference and tooling.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com>
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>