mtd: rawnand: lpc32xx_slc: switch to using gpiod API

This switches the driver from legacy gpio API to a newer gpiod API.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20220928230019.2140896-2-dmitry.torokhov@gmail.com