Add xpu header to include/ATen/xpu (#120786)
# Motivation
Add xpu header file to `include/ATen/xpu` to make them public.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/120786
Approved by: https://github.com/gujinghui, https://github.com/EikanWang, https://github.com/jgong5, https://github.com/albanD
