MIPS: [turbofan] Also optimize unsigned division by constant.

Port r25061 (7fe697f)

TEST=cctest,mjsunit,unittests
BUG=
R=paul.lind@imgtec.com

Review URL: https://codereview.chromium.org/701543002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25081 ce2b1a6d-e550-0410-aec6-3dcde31c8c00