mtd: nand: omap2: Remove omap_nand_platform_data

As driver is now configured using DT, omap_nand_platform_data structure
is no longer needed.

Signed-off-by: Ladislav Michl <ladis@linux-mips.org>
Acked-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>