Currently allocation in generated code on ARM is only used for allocating heap numbers. This change factors this out for use in upcomming changes.
Review URL: http://codereview.chromium.org/173625

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2789 ce2b1a6d-e550-0410-aec6-3dcde31c8c00