[llvm] [GlobalISel][AArch64] Add lowering for G_UMULFIX (PR #197018)

[Gábor Spaits via llvm-commits]

spaits wrote:

I have also created a PR for the sat versions of these opcodes: G_SMULFIXSAT and G_UMULFIXSAT (#197400). Those PRs depend on those. If all these are merged GISel won't fail for `@llvm.[u|s]mul(.sat)?.fix.*` intrinsics.

https://github.com/llvm/llvm-project/pull/197018