Cleanup of x64 code.  Rearrange functions in ic-x64.cc to match order in ic-ia32.cc.  Remove unused declarations, and move a constant to assembler-x64.h.
Review URL: http://codereview.chromium.org/6020012

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6143 ce2b1a6d-e550-0410-aec6-3dcde31c8c00