Introduce Armada 38x/XP network controller support

This patch contains a new driver for the network unit of Marvell
Armada 38x/XP SoCs, called NETA. This support was thoroughly tested
and optimised in terms of stability and performance. Additional
hardware features, like Buffer Management (BM) or Parser and Classifier
(PnC) will be progressively supported as needed.

Submitted by: Fabien Thomas <fabien.thomas@stormshield.eu>

	      Arnaud Ysmal <arnaud.ysmal@stormshield.eu>
	      Zbigniew Bodek <zbb@semihalf.com>
	      Michal Mazur <mkm@semihalf.com>
	      Bartosz Szczepanek <bsz@semihalf.com>
	      Marcin Wojtas <mw@semihalf.com>

Obtained from: Semihalf
Sponsored by: Stormshield (main development)

		Netgate (cleanup and upstreaming)

Differential revision: https://reviews.freebsd.org/D10706