[clang] [amdgpu-arch] Replace use of HSA with reading sysfs directly (PR #116651)

[Jon Chesterfield via cfe-commits]

https://github.com/JonChesterfield approved this pull request.

Absolutely yes, awesome. I had a todo to have the kernel export this under sysfs literally years ago and didn't get around to working out their commit structure, delighted to see it is exposed. The unreliable hsa calls has been a consistent nuisance for ages, great to see we don't need that hack any more.

Possible after-commit fix is to replace all the return 1 with different numbers (maybe an enum?) so that we have exit 0 on success and an exit code which indicates what went wrong on failure.

https://github.com/llvm/llvm-project/pull/116651