[llvm] [CodeGen] computeRegisterProperties - fix `bf16` to `i16` bitcast quieting NaNs (PR #224867)

[Trevor Gross via llvm-commits]

tgross35 wrote:

Are backports still being accepted for the current release branch? I assume this would be considered too large to backport as-is, but perhaps if amdgcn changes could be pushed to a followup PR and the remaining x86/rv64 fixes could make it to release.

https://github.com/llvm/llvm-project/pull/224867