ARM: Make use of d16-d31 when available.

Review URL: https://chromiumcodereview.appspot.com/11428137
Patch from Hans Wennborg <hans@chromium.org>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13484 ce2b1a6d-e550-0410-aec6-3dcde31c8c00