[llvm] [AArch64][GlobalISel] Select UMULL instruction (PR #65469)

[David Green via llvm-commits]

https://github.com/davemgreen commented:

>From what I can tell this looks OK. The expanded v2i64 muls are a little less optimized in places as the legalization artefact combiners haven't kicked in. That is probably something that could be improved with some other targeted optimizations.
@aemerson any thoughts?

https://github.com/llvm/llvm-project/pull/65469