Add the SPDX license identifier GPL-3.0-or-later to the header of all
scripts without a specific license and upgrading those that are stated
as GPL-2.0 to become GPL-3.0-or-later.
Transform sogrep into an in-prog so we can benefit from the m4 macro
to specify valid repos in a single place of truth.
Signed-off-by: Levente Polyak <anthraxx@archlinux.org>