ARM: dts: am571x-idk: enable for new cpsw switch dev driver

Add DT nodes for new cpsw switchdev driver for am571x-idk board for now to
enable testing of the new solution.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>