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 AM335x Chiliboard 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>