MIPS: Refactor BinaryOpIC to be able to use different stubs.

MIPS: Refactor BinaryOpIC to be able to use different stubs.

Port r18191 (c20c6dc1)

Original commit message:
Previously BinaryOpIC and BinaryOpStub were pretty much interdependent.
However, in order to use allocation sites for string adds on-demand,
we need to be able to use different stubs (with a different number of
register parameters, via trampolines) depending on the BinaryOpIC state.

BUG=
R=plind44@gmail.com

Review URL: https://codereview.chromium.org/100023002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@18213 ce2b1a6d-e550-0410-aec6-3dcde31c8c00