[mips] Range check simm16

Summary:
There are too many instructions to exhaustively test so addiu and lwc2 are
used as representative examples.

It should be noted that many memory instructions that should have simm16
range checking do not because it is also necessary to support the macro
of the same name which accepts simm32. The range checks for these occur in
the macro expansion.

Reviewers: vkalintiris

Subscribers: dsanders, llvm-commits

Differential Revision: http://reviews.llvm.org/D18437

llvm-svn: 265019