[llvm] [AArch64] Improve lowering of truncating uzp1 (PR #82457)

[Mehdi Amini via llvm-commits]

joker-eph wrote:

I see two Aarch64 tests consistently failing on the bot after this change: https://lab.llvm.org/buildbot/#/builders/272/builds/11141

https://github.com/llvm/llvm-project/pull/82457