[turbofan] Also optimize unsigned division by constant.

TEST=cctest,mjsunit,unittests
R=jarin@chromium.org

Review URL: https://codereview.chromium.org/697663003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25061 ce2b1a6d-e550-0410-aec6-3dcde31c8c00