AUTHORS: Move src/arch/arm64 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:
- Make sure files say that they're part of the coreboot project
- Move descriptions below the license header

Note that the file include/arch/acpi.h is a fantastic example of why
moving to the authors file is needed.  Excluding the guard statements,
it has 8 lines of copyrights for 3 function declarations.

Signed-off-by: Martin Roth <martin@coreboot.org>
Change-Id: I334baab2b4311eb1bd9ce3f67f49a68e8b73630c
Reviewed-on: https://review.coreboot.org/c/coreboot/+/34606
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/arch/arm64/div0.c

@@ -1,6 +1,5 @@
 /*
- * (C) Copyright 2002
- * Wolfgang Denk, DENX Software Engineering, wd@denx.de.
+ * This file is part of the coreboot project.
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License as