Also unify the handling of binops in the InstructionSelector
backends.

TEST=cctest/test-run-machops,cctest/test-instruction-selector-arm
R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/415403005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22800 ce2b1a6d-e550-0410-aec6-3dcde31c8c00