Accepting torch device objects in the Pipeline init 
### Feature request

Currently Pipeline init only takes an integer as a device argument in the constructor. It would make it a little easier to interface with and integrate with existing code if it also took a pytorch device object. 

### Motivation

It's frustrating not be to be able to use the model.device/self.device object when instantiating the pipeline object 

### Your contribution

I feel like I could do this and I'm happy to take a whack, but I haven't contributed to Transformers yet 
cc @Narsil <|||||>@courtneysprouse you're entirely correct, there's no real reason why we don't accept those.

The reason why we want to be able to accept `int` is to support seamless `TF` and `PyTorch` (which don't use the same conventions for devices) but the pipeline abstracts that away. But if you want to use native objects, you should always be able to for sure.<|||||>Awesome! Thank you so much!