AUTHORS: Move src/arch/ppc64 copyrights into AUTHORS file

As discussed on the mailing list and voted upon, the coreboot project
is going to move the majority of copyrights out of the headers and into
an AUTHORS file.  This will happen a bit at a time, as we'll be unifying
license headers at the same time.

Additional changes in this patch:
- Move descriptions below the license header

Signed-off-by: Martin Roth <martin@coreboot.org>
Change-Id: I51d5b1f01ff47ed752761116e3f32cb9e168584f
Reviewed-on: https://review.coreboot.org/c/coreboot/+/34637
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: Werner Zeh <werner.zeh@siemens.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/arch/ppc64/boot.c

@@ -1,8 +1,6 @@
 /*
  * This file is part of the coreboot project.
  *
- * Copyright 2013 Google Inc.
- *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Software Foundation; version 2 of the License.