Enable multi-device for efficientnet
Author: jla524
Pull request: yes

# What does this PR do?

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Fixes #29786 (issue)

Tested on two systems, one with 2x RTX 3060 and one with 2x RTX 3090

```
$ pytest tests/models/efficientnet/test_modeling_efficientnet.py -k "parallel or offload"
=================================================================== test session starts ===================================================================
platform linux -- Python 3.10.13, pytest-7.4.4, pluggy-1.4.0
rootdir: /repos/transformers
configfile: pyproject.toml
plugins: hypothesis-6.98.10, xdist-3.5.0, timeout-2.3.1, anyio-4.3.0
collected 108 items / 101 deselected / 7 selected                                                                                                         

tests/models/efficientnet/test_modeling_efficientnet.py .......                                                                                     [100%]

<warnings redacted>
===================================================== 7 passed, 101 deselected, 12 warnings in 8.85s ======================================================
```

## Who can review?

@amyeroberts 

<!-- Your PR will be replied to more quickly if you can figure out the right person to tag with @

 If you know how to use git blame, that is the easiest way, otherwise, here is a rough guide of **who to tag**.
 Please tag fewer than 3 people.

Models:

- text models: @ArthurZucker and @younesbelkada
- vision models: @amyeroberts
- speech models: @sanchit-gandhi
- graph models: @clefourrier

Library:

- flax: @sanchit-gandhi
- generate: @gante
- pipelines: @Narsil
- tensorflow: @gante and @Rocketknight1
- tokenizers: @ArthurZucker
- trainer: @muellerzr and @pacman100

Integrations:

- deepspeed: HF Trainer/Accelerate: @pacman100
- ray/raytune: @richardliaw, @amogkam
- Big Model Inference: @SunMarc
- quantization (bitsandbytes, autogpt): @SunMarc and @younesbelkada

Documentation: @stevhliu and @MKhalusova

HF projects:

- accelerate: [different repo](https://github.com/huggingface/accelerate)
- datasets: [different repo](https://github.com/huggingface/datasets)
- diffusers: [different repo](https://github.com/huggingface/diffusers)
- rust tokenizers: [different repo](https://github.com/huggingface/tokenizers)

Maintained examples (not research project or legacy):

- Flax: @sanchit-gandhi
- PyTorch: See Models above and tag the person corresponding to the modality of the example.
- TensorFlow: @Rocketknight1

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