mtd: nand: fsmc: remove unused definitions

These definitions are not used anywhere in the driver, so remove them.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>