[llvm] [SelectionDAG] Legalize vector types for atomic load (PR #111414)

[via llvm-commits]

jofrn wrote:

| Do stores also need to be handled?
No, they do not.
| No disable-verify
Rebased this on top of https://github.com/llvm/llvm-project/pull/117625.

https://github.com/llvm/llvm-project/pull/111414