ARM: dts: am335x-nano: switch to new cpsw switch drv

The dual_mac mode has been preserved the same way between legacy and new
driver, and one port devices works the same as 1 dual_mac port - it's safe
to switch drivers.

So, switch Newflow AM335x NanoBone to use new cpsw switch driver. Those
boards have or 2 Ext. port wired and configured in dual_mac mode by
default, or only 1 Ext. port.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>