MIPS: Use IC register definitions in platform files.

Port r22035 (0eac506)

BUG=
R=palfia@homejinni.com

Review URL: https://codereview.chromium.org/354013003

Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22044 ce2b1a6d-e550-0410-aec6-3dcde31c8c00