security/seclists: Add license files
- Restore LICENSE_FILE for GPLv2+ that was removed with commit 4acd06ebacdd0f134372d7fa390064ff4a4dfcf1, as the note about avoiding installing GPL licenses in section 13.20 of the Porter's handbook has been removed by commit e3f1471c227dfc4a557286072a020e62856bf0d9 of the doc repository.
- Add LICENSE_FILE for GPLv2.
Approved by: gerald (mentor)