Tiny params.

def img2img_transformer_tiny():
  """Tiny params."""
  hparams = img2img_transformer2d_base()
  hparams.num_hidden_layers = 2
  hparams.hidden_size = 128
  hparams.batch_size = 4
  hparams.max_length = 128
  hparams.attention_key_channels = hparams.attention_value_channels = 0
  hparams.filter_size = 128
  hparams.num_heads = 1
  hparams.pos = "timing"
  return hparams