Allow for specify coda device in perplexity evaluation

The current implementation of `perplexity.compute` does not allow to provide a specific coda device (e.g. `cuda:1` instead of just `cuda`.

https://github.com/huggingface/evaluate/blob/8dfe05784099fb9af55b8e77793205a3b7c86465/metrics/perplexity/perplexity.py#L108

Should probably be changed to something along the lines of:
```python
assert device in ["gpu", "cpu", "cuda"] or re.search(r'^cuda:[0-9]+$', device), "device should be either gpu or cpu."
```