MIPS: Rename AllocationSite::payload to AllocationSite::transition_info

Port r15556 (3cd37fff)

BUG=

Review URL: https://codereview.chromium.org/18615008

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15563 ce2b1a6d-e550-0410-aec6-3dcde31c8c00