[llvm] [PowerPC] Support conversion between f16 and f128 (PR #97677)

[via llvm-commits]

EsmeYi wrote:

> Should tests at [`f128-conv.ll`](https://github.com/llvm/llvm-project/blob/ad82d1c53f089937c05af11ff45798ceb5ca894e/llvm/test/CodeGen/PowerPC/f128-conv.ll) or [`fp128-libcalls.ll`](https://github.com/llvm/llvm-project/blob/ad82d1c53f089937c05af11ff45798ceb5ca894e/llvm/test/CodeGen/PowerPC/fp128-libcalls.ll) be updated?

Thank you @tgross35. Sorry that I missed the comment before. I've updated the 2 tests and removed llvm/test/CodeGen/PowerPC/f16-to-from-f128.ll, since it was redundant then.

https://github.com/llvm/llvm-project/pull/97677