`load_tf_weights` doesn't handle the weights added to the TF models at the top level
### System Info

- `transformers` version: 4.22.0.dev0
- Platform: Windows-10-10.0.22000-SP0
- Python version: 3.9.11
- Huggingface_hub version: 0.8.1
- PyTorch version (GPU?): 1.12.1+cu113 (True)
- Tensorflow version (GPU?): 2.9.1 (False)
- Flax version (CPU?/GPU?/TPU?): not installed (NA)
- Jax version: not installed
- JaxLib version: not installed
- Using GPU in script?: No
- Using distributed or parallel set-up in script?: No

### Who can help?

@gante

### Reproduction

(TF)MarianMTModel has weights `final_logits_bias` added at the top-level (i.e. not under any layer)

https://github.com/huggingface/transformers/blob/5f06a09b9f3f05b4860f11bbbe22861923b49d81/src/transformers/models/marian/modeling_tf_marian.py#L1287

However, the method `load_tf_weights` only handle weights under some layers

https://github.com/huggingface/transformers/blob/5f06a09b9f3f05b4860f11bbbe22861923b49d81/src/transformers/modeling_tf_utils.py#L850

This causes problem when we load TF checkpoints for `TFMarianMTModel`, i.e. `final_logits_bias` is not loaded.

```python
from transformers import MarianMTModel, TFMarianMTModel
model_name = "Helsinki-NLP/opus-mt-en-ROMANCE"

pt_model = MarianMTModel.from_pretrained(model_name)
tf_model_from_pt = TFMarianMTModel.from_pretrained(model_name, from_pt=True)
tf_model = TFMarianMTModel.from_pretrained(model_name, from_pt=False)

# Only has `TFMarianMainLayer` in `layers`
print(tf_model.layers)

print(pt_model.final_logits_bias.numpy())
print(tf_model_from_pt.final_logits_bias.numpy())
print(tf_model.final_logits_bias.numpy())
```

Outputs:

```bash
[<transformers.models.marian.modeling_tf_marian.TFMarianMainLayer object at 0x000001F00ECE9940>]
[[11.757146  -1.7759448 -7.3816853 ... -1.6559223 -1.6663467  0.       ]]
[[11.757146  -1.7759448 -7.3816853 ... -1.6559223 -1.6663467  0.       ]]
[[0. 0. 0. ... 0. 0. 0.]]
```


### Expected behavior

`load_tf_weights` should be able to load weights like `final_logits_bias`, and the TF checkpoint should be loaded correctly.
Related to #18149.<|||||>cc @patrickvonplaten as we might need to change the core method `load_tf_weights`.