mtd: nand: omap: Use gpmc_omap_get_nand_ops() to get NAND registers

Deprecate nand register passing via platform data and use
gpmc_omap_get_nand_ops() instead.

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