Cleanup the MIPS tunings to match the new tuning README file. Also
add a MIPS specific README file to explain the MIPS specifical
architectural issues.
Finally correct the variant configurations within the tune-mips32.inc.
(From OE-Core rev: efbfa2ace3362393a20340af93e8dcab17a8619a)
Signed-off-by: Mark Hatle <mark.hatle@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
