Small single parameters.

def mtf_image_transformer_single():
  """Small single parameters."""
  hparams = mtf_image_transformer_tiny()
  hparams.mesh_shape = ""
  hparams.layout = ""
  hparams.hidden_size = 32
  hparams.filter_size = 32
  hparams.batch_size = 1
  hparams.num_encoder_layers = 1
  hparams.num_decoder_layers = 1
  hparams.num_heads = 2
  hparams.attention_key_size = 32
  hparams.attention_value_size = 32
  hparams.block_length = 16
  return hparams