Move code stub implementations from codegen-[platform].cc files to new code-stub-[platform].cc files, and declarations to new code-stub-[platform].h files.
Remaining work is to do the same for platform-independent code stub declarations, and to remove all dependencies on codegen header files from code stub files.
Review URL: http://codereview.chromium.org/3195022

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5338 ce2b1a6d-e550-0410-aec6-3dcde31c8c00