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

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 <[email protected]>
Reviewed-by: Philippe Ombredanne <[email protected]>
Reviewed-by: Kate Stewart <[email protected]>
Reviewed-by: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Jonathan Corbet <[email protected]>