LICENSES/GPL2.0: Add GPL-2.0-only/or-later as valid identifiers

Quite some files have been flagged with the new GPL-2.0-only and
GPL-2.0-or-later identifiers which replace the original GPL-2.0 and
GPL-2.0+ identifiers in the SPDX license identifier specification, but the
identifiers are not mentioned as valid in the GPL-2.0 license file.

Add them to the license file and to the Linux-syscall-note exception to
make everything consistent again.

Signed-off-by: Thomas Gleixner <[e-mail]>
Reviewed-by: Greg Kroah-Hartman <[e-mail]>
Reviewed-by: Mauro Carvalho Chehab <[e-mail]>
Cc: Hans Verkuil <[e-mail]>
Signed-off-by: Jonathan Corbet <[e-mail]>

LICENSES/exceptions/Linux-syscall-note

···
 SPDX-Exception-Identifier: Linux-syscall-note
 SPDX-URL: https://spdx.org/licenses/Linux-syscall-note.html
-SPDX-Licenses: GPL-2.0, GPL-2.0+, GPL-1.0+, LGPL-2.0, LGPL-2.0+, LGPL-2.1, LGPL-2.1+
+SPDX-Licenses: GPL-2.0, GPL-2.0+, GPL-1.0+, LGPL-2.0, LGPL-2.0+, LGPL-2.1, LGPL-2.1+, GPL-2.0-only, GPL-2.0-or-later
 Usage-Guide:
   This exception is used together with one of the above SPDX-Licenses
   to mark user space API (uapi) header files so they can be included

LICENSES/preferred/GPL-2.0

···
 Valid-License-Identifier: GPL-2.0
+Valid-License-Identifier: GPL-2.0-only
 Valid-License-Identifier: GPL-2.0+
+Valid-License-Identifier: GPL-2.0-or-later
 SPDX-URL: https://spdx.org/licenses/GPL-2.0.html
 Usage-Guide:
   To use this license in source code, put one of the following SPDX
···
   guidelines in the licensing rules documentation.
   For 'GNU General Public License (GPL) version 2 only' use:
     SPDX-License-Identifier: GPL-2.0
+  or
+    SPDX-License-Identifier: GPL-2.0-only
   For 'GNU General Public License (GPL) version 2 or any later version' use:
     SPDX-License-Identifier: GPL-2.0+
+  or
+    SPDX-License-Identifier: GPL-2.0-or-later
 License-Text:
 
 		    GNU GENERAL PUBLIC LICENSE