net: netcp: Add Keystone NetCP core ethernet driver

The network coprocessor (NetCP) is a hardware accelerator available in
Keystone SoCs that processes Ethernet packets. NetCP consists of following
hardware components

 1 Gigabit Ethernet (GbE) subsystem with a Ethernet switch sub-module to
   send and receive packets.
 2 Packet Accelerator (PA) module to perform packet classification
   operations such as header matching, and packet modification operations
   such as checksum generation.
 3 Security Accelerator(SA) capable of performing IPSec operations on
   ingress/egress packets.
 4 An optional 10 Gigabit Ethernet Subsystem (XGbE) which includes a
   3-port Ethernet switch sub-module capable of 10Gb/s and 1Gb/s rates
   per Ethernet port.
 5 Packet DMA and Queue Management Subsystem (QMSS) to enqueue and dequeue
   packets and DMA the packets between memory and NetCP hardware components
   described above.

NetCP core driver make use of the Keystone Navigator driver API to allocate
DMA channel for the Ethenet device and to handle packet queue/de-queue,
Please refer API's in include/linux/soc/ti/knav_dma.h and
drivers/soc/ti/knav_qmss.h for details.

NetCP driver consists of NetCP core driver and at a minimum Gigabit
Ethernet (GBE) module (1) driver to implement the Network device function.
Other modules (2,3) can be optionally added to achieve supported hardware
acceleration function. The initial version of the driver include NetCP
core driver and GBE driver modules.

Please refer Documentation/devicetree/bindings/net/keystone-netcp.txt
for design of the driver.

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