net: ethernet: ti: am65-cpsw: add support for am64x cpsw3g

The TI AM64x SoCs Gigabit Ethernet Switch subsystem (CPSW3g NUSS) has three
ports (2 ext. ports) and provides Ethernet packet communication for the
device and can be configured in multi port mode or as an Ethernet switch.

This patch adds support for the corresponding CPSW3g version.

Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>