[SelectionDAG][AArch64] Legalize FMAXIMUM/FMINIMUM

The missing legalization in SelectionDAG was identified when adding the
intrinsic support for vector reduction for maximum/minimum (D152370).

Fixes part of PR: https://github.com/llvm/llvm-project/issues/63267

Differential Revision: https://reviews.llvm.org/D152718