A64: Cleaning of Builtins::Generate_FunctionCall.

This is mostly register renaming, and a minor optimization merging two TBZ into
one TST and BNE.

R=jochen@chromium.org

Review URL: https://codereview.chromium.org/166833002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@19428 ce2b1a6d-e550-0410-aec6-3dcde31c8c00