net/iavf: add basic NEON Rx

net/iavf: add basic NEON Rx

This patch adds the basic NEON Rx path to the iavf driver. It does not
include scatter or flex varieties.

Tested on N1SDP platform with Intel XL710 NIC and 40G connection.
Tested with a single core and testpmd rxonly mode. Saw no significant
performance difference between scalar and Arm vPMD paths using this test
in iavf and saw the same results when comparing scalar and Arm vPMD
path in i40e.

Signed-off-by: Kathleen Capella <kathleen.capella@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
Reviewed-by: Qi Zhang <qi.z.zhang@intel.com>