[mips] Fix encoding of the `mov.d` command for microMIPS R6

Before this change LLVM emits non-microMIPS variant of the `mov.d`
command for microMIPS code.

Differential Revision: http://reviews.llvm.org/D59045

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@356052 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed