[llvm] [CodeGen] Update for scalable MemoryType in MMO (PR #70452)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> I was thinking that would depend on whether the number of vector elements is assumed to always be the same between MMO and load type. i.e. the MMO could just store the size of the loaded memory, the load might extend each vector element. I'm not sure if there are somehow times when the types do not match?

The cases get ambiguous with sub-byte element vectors 

https://github.com/llvm/llvm-project/pull/70452