Code cleanup: reorder functions in codegen-x64.cc to agree with the order in...

Code cleanup: reorder functions in codegen-x64.cc to agree with the order in codegen-ia32.cc.  If svn blame shows this change, run svn blame on the previous version of the file to find the actual author of the lines.
Review URL: http://codereview.chromium.org/2955004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5040 ce2b1a6d-e550-0410-aec6-3dcde31c8c00