mips64: detect Cavium Octeon II in mips_features

Detect Cavium Octeon II CPU. This is needed as a prerequisite for
successful execution of cavium-octeon2 specific tests.

Patch by Zahid Anwar.

Related to Bugzilla issue 326444.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13782 a5019735-40e9-0310-863c-91ae7b9d1cf9