[FA2] Add flash attention for for DistilBert (#26489)

* flash attention added for DistilBert

* fixes

* removed padding_masks

* Update modeling_distilbert.py

* Update test_modeling_distilbert.py

* style fix

docs/source/en/model_doc/distilbert.md

@@ -133,6 +133,37 @@ A list of official Hugging Face and community (indicated by 🌎) resources to h
 - A blog post on how to [deploy DistilBERT with Amazon SageMaker](https://huggingface.co/blog/deploy-hugging-face-models-easily-with-amazon-sagemaker).
 - A blog post on how to [Deploy BERT with Hugging Face Transformers, Amazon SageMaker and Terraform module](https://www.philschmid.de/terraform-huggingface-amazon-sagemaker).
 
+
+## Combining DistilBERT and Flash Attention 2
+
+First, make sure to install the latest version of Flash Attention 2 to include the sliding window attention feature.
+
+```bash
+pip install -U flash-attn --no-build-isolation
+```
+
+Make also sure that you have a hardware that is compatible with Flash-Attention 2. Read more about it in the official documentation of flash-attn repository. Make also sure to load your model in half-precision (e.g. `torch.float16`)
+
+To load and run a model using Flash Attention 2, refer to the snippet below:
+
+```python
+>>> import torch
+>>> from transformers import AutoTokenizer, AutoModel
+
+>>> device = "cuda" # the device to load the model onto
+
+>>> tokenizer = AutoTokenizer.from_pretrained('distilbert-base-uncased')
+>>> model = AutoModel.from_pretrained("distilbert-base-uncased", torch_dtype=torch.float16, use_flash_attention_2=True)
+
+>>> text = "Replace me by any text you'd like."
+
+>>> encoded_input = tokenizer(text, return_tensors='pt').to(device)
+>>> model.to(device)
+
+>>> output = model(**encoded_input)
+```
+
+
 ## DistilBertConfig
 
 [[autodoc]] DistilBertConfig