package/swupdate: update license files

COPYING contains only the license for GPL-2.0 so use the new license
files that have been added in the Licenses directory since version
2018.03 and
https://github.com/sbabic/swupdate/commit/32c1f98eaca69e362be074197f84a59d994c0876

Also update GPL-2.0+ to "GPL-2.0+ with OpenSSL exception" and add
Exceptions file, see:
https://github.com/sbabic/swupdate/commit/66d0dbe80f49eb49f8999c9d738579651fc38134



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>