mips: update README.mips and NEWS for 3.9

Minor update to README.mips and NEWS section to state that MIPS64 support is
new in 3.9, as well as support for MIPS DSP ASE on MIPS32.



git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13661 a5019735-40e9-0310-863c-91ae7b9d1cf9
NEWS: Add info about bugs #316181 and #316696

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13662 a5019735-40e9-0310-863c-91ae7b9d1cf9
Remove autotools requirement as it is not specific to s390.
Minor wording changes.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13663 a5019735-40e9-0310-863c-91ae7b9d1cf9