[llvm] [AArch664] Replace uaddlv with addv for popcount operation (PR #121934)

[Cullen Rhodes via llvm-commits]

https://github.com/c-rhodes approved this pull request.

thanks Usha, left one small question for one of the tests but otherwise LGTM cheers. Also, please could you fix the typo in commit message `s/AArch664/AArch64`

https://github.com/llvm/llvm-project/pull/121934