PPC: [runtime] Introduce a proper %NewArray runtime entry.

Port ceade6cf

Original commit message:
    This adds a new %NewArray runtime entry, which constructs a new JSArray
    and does the subclassing correctly (to the same degree that %NewObject
    does currently), and also deals properly with the AllocationSite
    feedback mechanism. This runtime entry will be used by TurboFan and is
    also used as a fallback in the subclassing case in the stub currently.

R=bmeurer@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=v8:3101, v8:3330
LOG=n

Review URL: https://codereview.chromium.org/1466943002

Cr-Commit-Position: refs/heads/master@{#32180}

src/ppc/code-stubs-ppc.cc

@@ -5053,25 +5053,25 @@ void ArrayConstructorStub::Generate(MacroAssembler* masm) {
   GenerateDispatchToArrayStub(masm, DISABLE_ALLOCATION_SITES);
 
   __ bind(&subclassing);
-  __ push(r4);
-  __ push(r6);
-
-  // Adjust argc.
   switch (argument_count()) {
     case ANY:
     case MORE_THAN_ONE:
-      __ addi(r3, r3, Operand(2));
+      __ ShiftLeftImm(r0, r3, Operand(kPointerSizeLog2));
+      __ StorePX(r4, MemOperand(sp, r0));
+      __ addi(r3, r3, Operand(3));
       break;
     case NONE:
-      __ li(r3, Operand(2));
+      __ StoreP(r4, MemOperand(sp, 0 * kPointerSize));
+      __ li(r3, Operand(3));
       break;
     case ONE:
-      __ li(r3, Operand(3));
+      __ StoreP(r4, MemOperand(sp, 1 * kPointerSize));
+      __ li(r3, Operand(4));
       break;
   }
 
-  __ JumpToExternalReference(
-      ExternalReference(Runtime::kArrayConstructorWithSubclassing, isolate()));
+  __ Push(r6, r5);
+  __ JumpToExternalReference(ExternalReference(Runtime::kNewArray, isolate()));
 }