[clang] [llvm] [AMDGPU][WIP] Extend readlane, writelane and readfirstlane intrinsic lowering for generic types (PR #89217)

[Matt Arsenault via llvm-commits]

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

There should be no need to introduce same-sized value casts, whether bitcast or ptrtoint in either legalizer 

https://github.com/llvm/llvm-project/pull/89217