Harmonize naming a bit, x64 was the only platform where Register::from_code was called Register::toRegister.
Review URL: http://codereview.chromium.org/7364001

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8648 ce2b1a6d-e550-0410-aec6-3dcde31c8c00