Fix token_type_ids error for big_bird model.
I run the follow code, but get strange outputs, the `token_type_ids` is shorter than `input_ids`:
```python
def demo():
    model_name = "./resources/bigbird-roberta-base"
    tokenizer = AutoTokenizer.from_pretrained(model_name)
    text = 'With power of science ,'
    max_length = 10
    encoded_tokens = tokenizer.encode_plus(
        text=text,
        add_special_tokens=True,
        max_length=max_length,
        truncation=True if max_length is not None else False,
        return_tensors=None,
        return_offsets_mapping=tokenizer.is_fast,
        return_attention_mask=False,
        return_token_type_ids=True,
        return_special_tokens_mask=True,
    )
    print(encoded_tokens)
```
![CleanShot 2021-04-21 at 19 03 13@2x](https://user-images.githubusercontent.com/16603773/115543730-4b98be80-a2d4-11eb-8830-c1a2a20f4d84.png)
Seem it miss the `create_token_type_ids_from_sequences` method, so it run code in [here](https://github.com/huggingface/transformers/blob/95dab34d5588fb155dfed8293ac2fbb1217a95a7/src/transformers/tokenization_utils_base.py#L2665) as default. So I copy the method in BERT to fix it.

I know maybe the big_bird model doesn't need `token_type_ids`, but we also have to make sure it return the right result if we set `return_token_type_ids = True`. 
@sgugger <|||||>I think the BigBird QA model actually uses 16 token type ids (https://huggingface.co/google/bigbird-base-trivia-itc/blob/main/config.json), but this is an exception I think and the default case is 2 token type ids => so this looks good to me.

 @vasudevgupta7 what do you think?<|||||>Yes, both base & large pre-trained checkpoints accept 2 token type ids while only trivia-qa checkpoint accepts 16 token type ids. So, this should be good.