ARM: dts: am335x: Update elm phandle binding

The check for the "elm_id" binding had been removed.
This causes nand boot to fail on boards still using
the old binding. Update the bindings on those boards.

Signed-off-by: Teresa Remmet <t.remmet@phytec.de>
Acked-by: Brian Norris <computersforpeace@gmail.com>
Acked-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>