mtd: nand: gpio: Convert to use GPIO descriptors

mtd: nand: gpio: Convert to use GPIO descriptors

There is exactly one board in the kernel that defines platform data
for the GPIO NAND driver.

Use the feature to provide a lookup table for the GPIOs in the board
file so we can convert the driver as a whole to just use GPIO
descriptors.

After this we can cut the use of <linux/of_gpio.h> and use the GPIO
descriptor management from <linux/gpio/consumer.h> alone to grab and use
the GPIOs used in the driver.

I also created a local struct device *dev in the probe() function
because I was getting annoyed with all the &pdev->dev dereferencing.

Cc: [email protected]
Cc: Mike Rapoport <[email protected]>
Cc: Frans Klaver <[email protected]>
Cc: Gerhard Sittig <[email protected]>
Cc: Jamie Iles <[email protected]>
Signed-off-by: Linus Walleij <[email protected]>
Reviewed-by: Marek Vasut <[email protected]>
Acked-by: Jamie Iles <[email protected]>
Acked-by: Olof Johansson <[email protected]>
Acked-by: Robert Jarzmik <[email protected]>
Signed-off-by: Boris Brezillon <[email protected]>