[mips][msa] Updates encoding of 3RF instructions to match the latest revision of the MSA spec (1.06).

This does not affect any of the existing output.

Patch by Matheus Almeida


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191460 91177308-0d34-0410-b5e6-96231b3b80d8