Use instr mapping for microMIPS in llvm-mc.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194792 91177308-0d34-0410-b5e6-96231b3b80d8
Adding some info about stability of ARM boards

Patch by Mikael Lyngvig

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194794 91177308-0d34-0410-b5e6-96231b3b80d8