Enable autograd to recognize the XLA backend as one providing multiple devices (#17847)
Summary:
…e devices, while not being CUDA/HIP.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/17847
Differential Revision: D14545634
Pulled By: ezyang
fbshipit-source-id: 417181bf2ff4f8978544afe2fb6b042e787854ed
