message: Add tf._TPUDeviceOrdinalPlaceholder to TF MLIR ODS.
  This op will be used to represent a device ordinal that will be replaced when a tf_device.replicate op is expanded.
diff: @@ -1951,4 +1951,24 @@ def TF_CacheDatasetV2Op : TF_Op<"CacheDatasetV2", []> {
  );
  }
  +def TF__TPUDeviceOrdinalPlaceholderOp : TF_Op<"_TPUDeviceOrdinalPlaceholder", []> {
  + let summary = [{
  +Placeholder device ordinal that represents device ordinal of a replicated op.
  + }];
  +
  + let description = [{
  +This op can be used when certain rewrite passes materialize ops that require a
  +device ordinal of a replicated op but replication logic has been abstracted away
  +using tf_device.replicate op. Subsequent rewrite passes must replace this op with
  +a constant output that represents the correct device ordinal of the replicated
  +operations inside a TPU host.
  + }];
  +
  + let arguments = (ins);
  +
  + let results = (outs
  + TF_Int64Tensor:$device_ordinal
  + );
  +}
  +
  #endif // TF_OPS
  