Add MobileViT v2
### Model description

[MobileViT](https://openreview.net/forum?id=vh-0sUt8HlG) is a computer vision model that combines CNNs with transformers that has already been added to Transformers. 

[MobileViT v2](https://arxiv.org/abs/2206.02680) is the second version; it is constructed by replacing multi-headed self-attention in MobileViT v1 with the proposed separable self-attention. 

Does Hugging Face have plan to add MobileViT v2 to Transformers?

### Open source status

- [X] The model implementation is available
- [X] The model weights are available

### Provide useful links for the implementation

The official implementation is from Apple at this link: [https://github.com/apple/ml-cvnets](https://github.com/apple/ml-cvnets)

The timm library also implemented it and has pre-trained weights at this link: [https://github.com/huggingface/pytorch-image-models/blob/82cb47bcf360e1974c00c35c2aa9e242e6b5b565/timm/models/mobilevit.py](https://github.com/huggingface/pytorch-image-models/blob/82cb47bcf360e1974c00c35c2aa9e242e6b5b565/timm/models/mobilevit.py)

Hi @SunHaozhe , I would like to work on implementing this model.