[llvm] [AMDGPU] Add intrinsic for raw atomic buffer loads (PR #97707)

[via llvm-commits]

dyung wrote:

Two tests added in this commit seem to be failing on a build bot https://lab.llvm.org/buildbot/#/builders/174/builds/2102. Can you take a look and revert if you need time to investigate?

https://github.com/llvm/llvm-project/pull/97707