arch-arm: implement VMINNM and VMAXNM SIMD version

arch-arm: implement VMINNM and VMAXNM SIMD version

This instruction is backported from aarch64.

In order to use the existing fplibMinNum backend, we first move
VMIN and VPMIN to use fplib. Adding VMINNM is then trivial.

Change-Id: I404daabeb6079f60e51a648a06d5b3e54f1c24a9
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/18689
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>