[clang] [CIR][AArch64] Lower BF16 vduph lane builtins (PR #185852)

[Andrzej Warzyński via cfe-commits]

https://github.com/banach-space approved this pull request.

Thank you for addressing my comments,  LGTM %  the remaining (minor) comments

https://github.com/llvm/llvm-project/pull/185852