arm64: dts: ti: k3-j721e-mcu: add mcu cpsw nuss node

Add DT node for The TI J721E MCU SoC Gigabit Ethernet
subsystem (MCU CPSW NUSS).

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Tested-by: Murali Karicheri <m-karicheri2@ti.com>
Tested-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>