[mips][msa] Direct Object Emission of INSERT.{B,H,W} instruction.

[mips][msa] Direct Object Emission of INSERT.{B,H,W} instruction.

INSERT is the first type of MSA instruction that requires a change to the way
MSA registers are parsed. This happens because MSA registers may be suffixed by
an index in the form of an immediate or a general purpose register. The changes
to parseMSARegs reflect that requirement.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192582 91177308-0d34-0410-b5e6-96231b3b80d8