scripts: update SPDX license names
SPDX moved from GPL-2.0 to GPL-2.0-only and from GPL-2.0+ to
GPL-2.0-or-later. Reflect that in the SPDX license headers.
Signed-off-by: Paul Spooren <[email protected]>
[adjust commit title, update remaining files]
Signed-off-by: Adrian Schmutzler <[email protected]>