mips: adding MIPS64LE support to Valgrind

Necessary changes to Valgrind to support MIPS64LE on Linux.
Minor cleanup/style changes embedded in the patch as well.
The change corresponds to r2687 in VEX.
Patch written by Dejan Jevtic and Petar Jovanovic.

More information about this issue:
https://bugs.kde.org/show_bug.cgi?id=313267


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13292 a5019735-40e9-0310-863c-91ae7b9d1cf9