[turbofan][arm64] Optimize shifts combined with truncations or extensions.

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/705983002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25210 ce2b1a6d-e550-0410-aec6-3dcde31c8c00