[WIP] Add Efficientformer
# What does this PR do?

This PR adds Efficientformer, a model that has similar latency as MobileNets, but achieves better accuracy on ImageNet.

Paper: https://arxiv.org/abs/2206.01191
Code and weights: https://github.com/snap-research/EfficientFormer

To-do:

- [ ] Improve documentation
- [ ] Verify tests pass

Fixes #18041

## Who can review?

@NielsRogge 
This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md) are likely to be ignored.<|||||>Hi @novice03 @NielsRogge @alaradirik :) - what is the status of adding this model? @novice03 if you do not what to continue working on it I can pick it up from here.<|||||>Hi @Bearnardd, I'm afraid I don't have time in the next few weeks to continue working on this model. But, please pick it up from here if you can. Thanks!<|||||>Hi @alaradirik - I have just started working on this PR locally and I have applied most of the style changes that you have requested and in the following days I will apply the rest of the changes that you have asked for. Is there any possibility to catch you on Slack or on the other medium since I am pretty confident I will have some questions regarding this task. Thanks!<|||||>Hi @Bearnardd, of course, could you give me your email address? I can create a Slack channel and invite you.

If possible, it'd be great if @novice03 could add you as a collaborator to his transformers repo and you work on the same repo/branch so that he gets credit for the PR too.<|||||>Hi @alaradirik I have sent you my email address on LinkedIn also great idea about the collaboration. @novice03 if it suits you well you can send me an invitation :)<|||||>Hi @novice03 ! - I have done some work on top of your changes. Not everything is ready but I think that I am in good spot to push the changes and get some review before going further. Would you mind adding me as a collaborator to your repo so I can push there directly or do you want me to open a new PR on top of yours?<|||||>Hello @Bearnardd, I added you as a collaborator on my repo. Thanks!