MIPS: Improve integer multiplication.

Port r16576 (8ce78a4)

TEST=test/mjsunit/lithium/MulI.js
BUG=
R=plind44@gmail.com

Review URL: https://codereview.chromium.org/25050002

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

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16997 ce2b1a6d-e550-0410-aec6-3dcde31c8c00