Reland "MIPS: Add support for arch. revision 6 to mips32 port."

Fixing gclient runhooks failure caused by reverted commit r23050.

TEST=
BUG=
R=jkummerow@chromium.org, paul.lind@imgtec.com

Review URL: https://codereview.chromium.org/467583002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23088 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Merge remote-tracking branch 'upstream/master'