mtd: rawnand: sunxi: Remove gpio.h and of_gpio.h inclusions

Commit ddd5ed3a

 ("mtd: rawnand: sunxi: Remove support for
GPIO-based Ready/Busy polling") removed GPIO-based RB polling. We no
longer need to include gpio headers.

Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>