ARM: dts: am335x-myirtech: 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 MYIR MYC-AM335X/MYD-AM335X 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.

Cc: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>