MIPS: Unify some PlatformCodeStubs.

Port r23631 (87d82e2)

BUG=
R=dusan.milosavljevic@imgtec.com

Review URL: https://codereview.chromium.org/529203003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23654 ce2b1a6d-e550-0410-aec6-3dcde31c8c00