[mips] Guard 'nop' properly and add mips16's nop instruction

Reviewers: smaksimovic, atanasyan, abeserminji

Differential Revision: https://reviews.llvm.org/D47583


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@333739 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed