[llvm] [PowerPC] Conversions of f128 and f16 should use _kf_ instead of _tf_ (PR #99855)

[Trevor Gross via llvm-commits]

tgross35 wrote:

@chenzheng1030 would you be able to take a look at the second commit (40b97f3d5a5cfda323b84ffe89b42fe2ebd410c3) here, for merge after https://github.com/llvm/llvm-project/pull/97677?

https://github.com/llvm/llvm-project/pull/99855