mtd: rawnand: plat_nand: Kill pdata->ctrl.{hwcontrol, read_byte}()

None of the board files are overloading those hooks, so let's drop them
from struct platform_nand_ctrl.

Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>