[llvm] [AMDGPU] Add alignment attr & propagate alignment through make.buffer.rsrc inst (PR #145278)

[Matt Arsenault via llvm-commits]

arsenm wrote:

ptrmask shouldn't be any different than getelementptr: https://godbolt.org/z/nbe4x7qnd

It requires propagating the source attribute, and then interpreting it through the instruction to reach the return 

https://github.com/llvm/llvm-project/pull/145278