treewide: move copyrights and authors to AUTHORS

Also split "this is part of" line from copyright notices.

Change-Id: Ibc2446410bcb3104ead458b40a9ce7819c61a8eb
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41067
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: David Hendricks <david.hendricks@gmail.com>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>

src/include/b64_decode.h

@@ -1,6 +1,4 @@
 /*
- * Copyright (C) 2015 Google, Inc.
- *
  * This software is licensed under the terms of the GNU General Public
  * License version 2, as published by the Free Software Foundation, and
  * may be copied, distributed, and modified under those terms.