Add from_encoder_decoder_pretrained to some dummy obj
# What does this PR do?

Fix 

https://discuss.huggingface.co/t/flaxvisionencoderdecodermodel-decoder-start-token-id/13635

## Who can review?

@NielsRogge 
`check_dummies.py` need to be adjusted to make it work

https://github.com/huggingface/transformers/blob/9a94bb8e218033cffa1ef380010b528410ba3ca7/utils/check_dummies.py#L36-L52<|||||>Info: should not edit these dummy files manually

```
# This file is autogenerated by the command `make fix-copies`, do not edit.
```