LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers

Some files have been flagged with the new LGPL-2.1-or-later
identifier which replace the original LGPL-2.1+ in the SPDX license
identifier specification, but the identifiers are not mentioned as
valid in the LGPL-2.1 license file.

Add it, together with the LGPL-2.1-only at the the license file.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/12f38ebde4dcd8b1ecbd37df1b6ce2018426f6dd.1639657049.git.mchehab+huawei@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

LICENSES: Add the LGPL-2.1 license

Add the full text of the LGPL 2.1 license to the kernel tree. It was
copied directly from:

https://spdx.org/licenses/LGPL-2.1.html#licenseText

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>