net: ethernet: ti: Introduce am654 gigabit eth switch subsystem driver

Add new driver for the TI AM65x SoC Gigabit Ethernet Switch subsystem (CPSW
NUSS). It has two ports and provides Ethernet packet communication for the
device and can be configured as an Ethernet switch. CPSW NUSS features: the
Reduced Gigabit Media Independent Interface (RGMII), Reduced Media
Independent Interface (RMII), and the Management Data Input/Output (MDIO)
interface for physical layer device (PHY) management. The TI AM65x SoC has
integrated two-port Gigabit Ethernet Switch subsystem into device MCU
domain named MCU_CPSW0. One Ethernet port (port 1) with selectable RGMII
and RMII interfaces and an internal Communications Port Programming
Interface (CPPI) port (Host port 0).

Host Port 0 CPPI Packet Streaming Interface interface supports 8 TX
channels and on RX channels operating by TI am654 NAVSS Unified DMA
Peripheral Root Complex (UDMA-P) controller.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Keerthy <j-keerthy@ti.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>