MIPS: Allowed keyed store callbacks ic generation.

Port r19744 (b05fa4a)

BUG=
R=plind44@gmail.com

Review URL: https://codereview.chromium.org/191443007

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

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19767 ce2b1a6d-e550-0410-aec6-3dcde31c8c00