[mips][microMIPS] Implement disassembler support for 16-bit instructions LI16, ADDIUR1SP, ADDIUR2 and ADDIUS5

Differential Revision: http://reviews.llvm.org/D6419


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222887 91177308-0d34-0410-b5e6-96231b3b80d8