[llvm] [X86][LegalizeDAG] FPOWI: promote f16 operand (PR #105775)

[Phoebe Wang via llvm-commits]

phoebewang wrote:

`CodeGen/X86` since you changed the X86 backend code rather than generic code. Besides, some targets may have the test already.

https://github.com/llvm/llvm-project/pull/105775