net: netcp: Add Keystone NetCP GbE driver

This patch add support for 1G Ethernet driver based on Keystone
NetCP hardware. The gigabit Ethernet (GbE) switch subsystem is one of the main
components of the network coprocessor (NETCP) peripheral. The purpose of the
gigabit Ethernet switch subsystem in the NETCP is to provide an interface to
transfer data between the host device and another connected device in
compliance with the Ethernet protocol. GbE consists of 5 port Ethernet Switch
module, 4 Serial Gigabit Media Independent Interface (SGMII) modules, MDIO
module and SerDes.

Driver for 5 port GbE switch and SGMII module is added in this patch. These
hardware modules along with netcp core driver provides Network driver functions
for 1G Ethernet.

Detailed hardware spec is available at

http://www.ti.com/lit/ug/sprugv9d/sprugv9d.pdf

 Cc: David Miller <davem@davemloft.net>
 Cc: Rob Herring <robh+dt@kernel.org>
 Cc: Grant Likely <grant.likely@linaro.org>
 Cc: Santosh Shilimkar <santosh.shilimkar@kernel.org>
 Cc: Pawel Moll <pawel.moll@arm.com>
 Cc: Mark Rutland <mark.rutland@arm.com>
 Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
 Cc: Kumar Gala <galak@codeaurora.org>

Signed-off-by: Wingman Kwok <w-kwok2@ti.com>
Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>