MIPS: Improve code generation for bounds checks.

Port r20872 (0e79653)

BUG=
R=plind44@gmail.com

Review URL: https://codereview.chromium.org/246253007

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

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20892 ce2b1a6d-e550-0410-aec6-3dcde31c8c00