Add a kSimd128 machine type for Turbofan.

src/compiler/register-allocator.cc

Index: src/compiler/register-allocator.cc
diff --git a/src/compiler/register-allocator.cc b/src/compiler/register-allocator.cc
index 7610cd71015131f8a734601aa24f81b60759bba0..02ba1f17c24c640d6865f5c5805ec267b85828a6 100644
--- a/src/compiler/register-allocator.cc
+++ b/src/compiler/register-allocator.cc
@@ -104,6 +104,8 @@ int GetByteWidth(MachineRepresentation rep) {
     case MachineRepresentation::kWord64:
     case MachineRepresentation::kFloat64:
       return 8;
+    case MachineRepresentation::kSimd128:
+      return 16;
     case MachineRepresentation::kNone:
       break;
   }