mtd: nand: omap: Clean up device tree support

Move NAND specific device tree parsing to NAND driver.

The NAND controller node must have a compatible id, register space
resource and interrupt resource.

Signed-off-by: Roger Quadros <rogerq@ti.com>
Acked-by: Brian Norris <computersforpeace@gmail.com>
Acked-by: Tony Lindgren <tony@atomide.com>