This adapts all files that were identifed by licensecheck
(https://salsa.debian.org/build-common-team/licensecheck.git) as
licensed under the GPL and that have a (IMHO) clear copyright statement.

The advantage is that these specifiers are machine-parseable which helps
license conformance, e.g. for packaging barebox in Debian.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>