Revert of [Atomics] Remove Atomics code stubs; use TF ops

src/ppc/interface-descriptors-ppc.cc

Index: src/ppc/interface-descriptors-ppc.cc
diff --git a/src/ppc/interface-descriptors-ppc.cc b/src/ppc/interface-descriptors-ppc.cc
index 4dfb2bba662569cdd2ebd35d5fe11f4cd336ee93..4a4075934e780ffe6181825980bd8c6fd0574e27 100644
--- a/src/ppc/interface-descriptors-ppc.cc
+++ b/src/ppc/interface-descriptors-ppc.cc
@@ -420,6 +420,15 @@
   };
   data->InitializePlatformSpecific(arraysize(registers), registers);
 }
+
+void AtomicsLoadDescriptor::InitializePlatformSpecific(
+    CallInterfaceDescriptorData* data) {
+  Register registers[] = {
+      r4,  // the typedarray object
+      r3   // the index to load (untagged)
+  };
+  data->InitializePlatformSpecific(arraysize(registers), registers);
+}
 }  // namespace internal
 }  // namespace v8