Llama Tokenizer uses incorrect indices for PAD
### System Info

latest transformer main

### Who can help?

@gante

### Information

- [ ] The official example scripts
- [ ] My own modified scripts

### Tasks

- [X] An officially supported task in the `examples` folder (such as GLUE/SQuAD, ...)
- [ ] My own task or dataset (give details below)

### Reproduction

configuration_llama.py sets 
```
pad_token_id=0,
bos_token_id=1,
eos_token_id=2
```

but this is wrong. After checking the original tokenizer from FB,

```python
sp_model = SentencePieceProcessor(model_file="/home/ubuntu/llama/tokenizer.model")

print("bos_id: ", sp_model.bos_id())
print("eos_id: ", sp_model.eos_id())
print("pad_id: ", sp_model.pad_id())
```

we see that 

```
bos_id:  1
eos_id:  2
pad_id:  -1
```



### Expected behavior

```
bos_id:  1
eos_id:  2
pad_id:  -1
```

instead of 

```
pad_token_id=0,
bos_token_id=1,
eos_token_id=2
```
cc @ArthurZucker -- is this fixed in #22402 ?<|||||>This is probably not gonna be fixed with regard to the `configuration_llama`. 
However note that having the `sp_model` sending `-1` as a pad token means that it does not have any indices. Llama does not use a padding token. 
The fix that we provide is that in the `tokenization_llama` the `pad_token` is set to `None`. 

The config should be fixed to ensure that `pad_token=None` rather than `pad_token = 0`<|||||>Thanks @gante @ArthurZucker 

What about the mismatch between the eos and bos tokens? Or is HF's tokenizer zero-indexed while Meta's native tokenizer is one-indexed?<|||||>As you said and showed using the `sp_model`, 
> bos_id:  1
eos_id:  2

If you instantiate the tokenizer using [this](https://huggingface.co/hf-internal-testing/llama-tokenizer/tree/main) for example, it has the same ids so I am not sure I follow the problem? <|||||>@ArthurZucker if I want to batching then I have to manually add a pad_token. In this case how do I ensure that the pad_token_id is actually correct? I.e how do I get the tokenizer to set pad_tokens to 0 instead of 32000  that I am getting now, by using add_special_tokens like `add_special_tokens({'pad_token': '[PAD]'})`<|||||>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.<|||||>The problem is that `0` is already the `unk` token. The easiest way is to set the pad token to the unk token.
