net: add Hisilicon Network Subsystem support (config and documents)

The Hisilicon Network Subsystem is a long term evolution IP which is
supposed to be used in Hisilicon ICT SoC. The IP, which is called hns
for short, is a TCP/IP acceleration engine, which can directly decode
TCP/IP stream and distribute them to different ring buffers.

HNS can be configured to work on different mode for different scenario.
This patch make use only some of the mode to make it as standard
ethernet NIC. The other mode will be added soon.

The whole function has 4 kernel sub-modules:

hnae: the HNS acceleration engine framework. It provides a abstract
interface between the engine and the upper layers which make use of the
engine by ring buffer.

hns_enet_drv: a standard ethernet driver that base on the ring buffer.

hns_dsaf: one of the implementation of HNS acceleration engine, which is
applied on Hililicon hip05, Hi1610 and other later-on SoCs

hns_mdio: the mdio control to the PHY, used by acceleration engine

This submit add basic config and documents

Signed-off-by: huangdaode <huangdaode@hisilicon.com>
Signed-off-by: Kenneth Lee <liguozhu@huawei.com>
Signed-off-by: Yisen Zhuang <Yisen.Zhuang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>