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.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

LICENSES/preferred/LGPL-2.1

 Valid-License-Identifier: LGPL-2.1
+Valid-License-Identifier: LGPL-2.1-only
 Valid-License-Identifier: LGPL-2.1+
+Valid-License-Identifier: LGPL-2.1-or-later
 SPDX-URL: https://spdx.org/licenses/LGPL-2.1.html
 Usage-Guide:
   To use this license in source code, put one of the following SPDX