net/virtio: add election for packed vector NEON path

net/virtio: add election for packed vector NEON path

Add NEON vectorized path selection logic. Default setting comes from
vectorized devarg, then checks each criteria.

Packed ring vectorized neon path need:
    NEON is supported by compiler and host
    VERSION_1 and IN_ORDER features are negotiated
    mergeable feature is not negotiated
    LRO offloading is disabled

Signed-off-by: Joyce Kong <joyce.kong@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>