mtd: rawnand: omap2: move to exec_op interface

Stop using legacy interface and move to the exec_op interface.
Signed-off-by: Roger Quadros <rogerq@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20211209090458.24830-4-rogerq@kernel.org