[mips][msa] Added support for matching comparisons from normal IR (i.e. not intrinsics)

MIPS SelectionDAG changes:
* Added VCEQ, VCL[ET]_[SU] nodes to represent vector comparisons that produce a bitmask.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191286 91177308-0d34-0410-b5e6-96231b3b80d8