PPC: [turbofan] Add the TruncateFloat32ToInt32 operator to turbofan.

Port fc53eed1

Original commit message:
    The new operator converts a float32 input to int32 through truncation.

R=ahaas@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=

Review URL: https://codereview.chromium.org/1593333006

Cr-Commit-Position: refs/heads/master@{#33392}

src/compiler/ppc/instruction-selector-ppc.cc

@@ -1015,6 +1015,11 @@ void InstructionSelector::VisitTruncateFloat64ToInt32(Node* node) {
 }
 
 
+void InstructionSelector::VisitTruncateFloat32ToInt32(Node* node) {
+  return VisitRR(this, kPPC_DoubleToInt32, node);
+}
+
+
 #if V8_TARGET_ARCH_PPC64
 void InstructionSelector::VisitTruncateInt64ToInt32(Node* node) {
   // TODO(mbrandy): inspect input to see if nop is appropriate.