mtd: rawnand: sh_flctl: Convert to module_platform_driver()

The driver doesn't benefit from the advantages that
module_platform_driver_probe() allows (i.e. putting the probe function
in .init.text and the .remove function into .exit.text).
So use module_platform_driver() instead which allows to bind the driver
also after booting (or module loading) and unbinding via sysfs.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20231016103540.1566865-2-u.kleine-koenig@pengutronix.de