Expose `offload_buffers` parameter of `accelerate` to `PreTrainedModel.from_pretrained` method
Author: notsyncing
Pull request: yes

# What does this PR do?

This PR will expose the `offload_buffers` parameter of the `dispatch_model` method in `accelerate` to the `PreTrainedModel.from_pretrained`, then we can make the following code easier if we want to use this parameter:

```python
config = AutoConfig.from_pretrained(model_id)

with accelerate.init_empty_weights():
  empty_model = AutoModelForCausalLM.from_config(config)

device_map = accelerate.infer_auto_device_map(empty_model, max_memory={0: "4GB", "cpu": "128GB"}, dtype=torch.bfloat16, no_split_module_classes=["LlamaDecoderLayer"])

model = AutoModelForCausalLM.from_pretrained(model_id, device_map=device_map)
```

now simplifies to 

```python
model = AutoModelForCausalLM.from_pretrained(model_id, device_map="auto", max_memory={0: "4GB", "cpu": "128GB"}, dtype=torch.bfload16, offload_buffers=True)
```

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- [ ] Did you write any new necessary tests?


## Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
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Comments:
@muellerzr would you mind taking a look? thanks!