[mips] Range check simm32 and fold MIPS16's imm32 into simm32.

Summary:
At this point we should be able to enable IAS by default for O32 without
breaking check-all, or recursion.

Reviewers: vkalintiris

Subscribers: dsanders, llvm-commits

Differential Revision: http://reviews.llvm.org/D18439

llvm-svn: 265302