[clang] [llvm] [TargetParser] Add a list of Intel GPUs, and use it in offload-arch (PR #222072)

[Tom Honermann via cfe-commits]

https://github.com/tahonermann requested changes to this pull request.

I added two assert requests, but this looks good to me otherwise.

I like @srividya-sundaram's suggestion for terminology that distinguishes between the full IGCA "target" with IGCA level and IGCA suffix used to refer to the individual components.

https://github.com/llvm/llvm-project/pull/222072