Revert r18144, r18143.

MIPS: Fix register usage.

MIPS: Cleanup in the CallStubCompiler.

The original revisions r18131 and r18139 have been reverted.

TBR=palfia@homejinni.com

Review URL: https://codereview.chromium.org/96743002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18154 ce2b1a6d-e550-0410-aec6-3dcde31c8c00