MIPS: Implement flooring division by a constant via truncating division by a constant.

Port r20123 (31ab416)

BUG=
R=plind44@gmail.com

Review URL: https://codereview.chromium.org/206373004

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

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20135 ce2b1a6d-e550-0410-aec6-3dcde31c8c00