MIPS: Always use the LoadStubCompiler for Load handlers, also for keyedload handlers.

Port r22551 (0cc23b1)

BUG=
R=paul.lind@imgtec.com

Review URL: https://codereview.chromium.org/415623002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22570 ce2b1a6d-e550-0410-aec6-3dcde31c8c00