[mips][microMIPS] Implement BREAK16 and SDBBP16 instructions

Patch by Radovan Obradovic.

Differential Revision: http://reviews.llvm.org/D5048


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222900 91177308-0d34-0410-b5e6-96231b3b80d8