For instructions that are marked as calls we can use:

1. Fixed input registers

2. Use-at-start policy (register, memory or constant).

(Memory or constant would not need the use-at-start policy, but
not specifying use-at-start prevents the allocator from using
a register even if there is one available. That's why use-at-start
is required and guarded by assertion)
Review URL: http://codereview.chromium.org/6853010

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7616 ce2b1a6d-e550-0410-aec6-3dcde31c8c00