Enable Mellanox drivers (modules) on AArch64

Tested by Greg V with mlx5en on an Ampere eMAG instance at Packet.com on
c2.large.arm (with some additional uncommitted PCIe WIP).

PR: 237055
Submitted by: Greg V <greg@unrelenting.technology>
Reviewed by: hselasky
MFC after: 1 month
Differential Revision: https://reviews.freebsd.org/D19983