[turbofan] Fix MachineOperatorReducer to use JSGraph as well.

TEST=compiler-unittests,cctest
R=jarin@chromium.org

Review URL: https://codereview.chromium.org/526083002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23577 ce2b1a6d-e550-0410-aec6-3dcde31c8c00