Added support for LWU microMIPS instruction.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199315 91177308-0d34-0410-b5e6-96231b3b80d8
LL and SC decoder method fix.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199316 91177308-0d34-0410-b5e6-96231b3b80d8