[mips] First patch which adds support for micromips.

This patch adds support for recoded (meaning assembly-language compatible to
standard mips32) arithmetic 32-bit instructions.

Patch by Zoran Jovanovic.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179873 91177308-0d34-0410-b5e6-96231b3b80d8