Processor for implementing memory efficient attention using xFormers for the Custom Diffusion method.  
Args:
train_kv (`bool`, defaults to `True`):
Whether to newly train the key and value matrices corresponding to the text features.
train_q_out (`bool`, defaults to `True`):
Whether to newly train query matrices corresponding to the latent image features.
hidden_size (`int`, *optional*, defaults to `None`):
The hidden size of the attention layer.