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

AUTHORS: Move src/arch/mips 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:
- Remove comments saying that a file is based on another file from the
coreboot project.

Signed-off-by: Martin Roth <martin@coreboot.org>
Change-Id: If61689db67c58f0d66ab96ca749bfcd589935ce2
Reviewed-on: https://review.coreboot.org/c/coreboot/+/34607
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: Werner Zeh <werner.zeh@siemens.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>