MIPS: Simplify feedback vector creation and store in SharedFunctionInfo.

Port r21085 (782ce81)

LOG=N
BUG=v8:3212
R=plind44@gmail.com

Review URL: https://codereview.chromium.org/267433003

Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21098 ce2b1a6d-e550-0410-aec6-3dcde31c8c00