Add tf.data.experimental.prefetch_to_device to train_eval_atari.py for slightly better performance.
Add tf.data.experimental.prefetch_to_device to train_eval_atari.py for slightly better performance.

PiperOrigin-RevId: 239646439
Change-Id: I15487b21e946853d42f18fe64fb802654f3e59eb

tensorflow/agents,tensorflow/agents