[mips][msa] Implemented build_vector using ldi, fill, and custom SelectionDAG nodes (VSPLAT and VSPLATD)

Note: There's a later patch on my branch that re-implements this to select
build_vector without the custom SelectionDAG nodes. The future patch avoids
the constant-folding problems stemming from the custom node (i.e. it doesn't
need to re-implement all the DAG combines related to BUILD_VECTOR).

Changes to MIPS specific SelectionDAG nodes:
* Added VSPLAT
    This is a special case of BUILD_VECTOR that covers the case the
    BUILD_VECTOR is a splat operation.
* Added VSPLATD
    This is a special case of VSPLAT that handles the cases when v2i64 is legal


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191191 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/Mips/MipsISelLowering.cpp b/lib/Target/Mips/MipsISelLowering.cpp
index 220955e..21c5edb 100644
--- a/lib/Target/Mips/MipsISelLowering.cpp
+++ b/lib/Target/Mips/MipsISelLowering.cpp
@@ -212,6 +212,8 @@
   case MipsISD::VANY_ZERO:         return "MipsISD::VANY_ZERO";
   case MipsISD::VALL_NONZERO:      return "MipsISD::VALL_NONZERO";
   case MipsISD::VANY_NONZERO:      return "MipsISD::VANY_NONZERO";
+  case MipsISD::VSPLAT:            return "MipsISD::VSPLAT";
+  case MipsISD::VSPLATD:           return "MipsISD::VSPLATD";
   default:                         return NULL;
   }
 }