[c10d] Add xpu to the default device supported by user specified backend (#103410)
**Motivation:**
For collective dispatching, we want to provide a more user friendly usage for xpu device and CCL backend (user specified backend) mapping.
**Solution:**
We add xpu to the default device list, and it can construct the mapping between xpu and the user specified backend directly.
Usage:
When using xpu device, user can specify backend name only:
`dist.init_process_group(backend='ccl')`
Pull Request resolved: https://github.com/pytorch/pytorch/pull/103410
Approved by: https://github.com/jgong5, https://github.com/ezyang
