[AArch64] Match fminnum/fmaxnum for vector fminnm/fmaxnm instead of an intrinsic.

Lower Intrinsic::aarch64_neon_fmin/fmax to fminnum/fmannum and match that instead. Minimal functional change:

  - Extra tests added because coverage of scalar fminnm/fmaxnm instructions was nonexistant.
  - f16 test updated because now we actually generate scalar fminnm/fmaxnm we no longer need to bail out to a libcall!

llvm-svn: 244595