[llvm] [X86][NVPTX][LegalizeDAG] If i16 legal, legalize FABS.f16 with Expand (PR #106153)

[via llvm-commits]

v01dXYZ wrote:

@phoebewang I added also `FNEG`/`FCOPYSIGN`. I rewrote a little bit the code to avoid having special cases within `setF16Action` (not more efficient but simpler). 

https://github.com/llvm/llvm-project/pull/106153