[InstCombine] Guard against FP min/max in select fold (PR64937)

This is partial revert of cbca9ce9.
That commit removed the code guarding against min/max SPF patterns,
because those are now canonicalized to min/max intrinsics. However,
this is only true for integer min/max, while FP min/max can not
always be canonicalized to an intrinsic. As such, restore a
simplified version of the guard that handles only the FP case.

Fixes https://github.com/llvm/llvm-project/issues/64937.