[AArch64] Extend vecreduce -> udot handling to mla reductions

We previously have lowering for:
  vecreduce.add(zext(X)) to vecreduce.add(UDOT(zero, X, one))
This extends that to also handle:
  vecreduce.add(mul(zext(X), zext(Y)) to vecreduce.add(UDOT(zero, X, Y))
It extends the existing code to optionally handle a mul with equal
extends.

Differential Revision: https://reviews.llvm.org/D97280