[llvm] [AMDGPU] Implement getAddrSpaceCastPreservedPtrMask (PR #182658)

[Shilei Tian via llvm-commits]

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

LGTM, but let's wait for the final confirmation from @arsenm @jayfoad @rampitec 

https://github.com/llvm/llvm-project/pull/182658