ARM: dts: omap5-igep0050: Allow bootloader to configure USB Ethernet MAC

This is slightly different wiring compared to omap5-uevm or pandaboard:

/sys/bus/usb/devices/3-2	hub
/sys/bus/usb/devices/3-2.3	7500

Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>