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

Original commit r23028 breaks ARM64 build due to conflicting FP64 symbolic constant definition in src/globals.h and src/arm64/constants-arm64.h.

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

Review URL: https://codereview.chromium.org/457313003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23050 ce2b1a6d-e550-0410-aec6-3dcde31c8c00