mtd: rawnand: davinci: Inherit from nand_controller

Let's not rely on the dummy_controller embedded in nand_chip.legacy
and explicitly inherit from nand_controller instead.

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Tested-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200513172248.141402-1-boris.brezillon@collabora.com