ARM: dts: am335x-sl50: switch to new cpsw switch drv

ARM: dts: am335x-sl50: 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 Toby Churchill SL50 Series 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>