mtd: nand: fsmc: get rid of IO_ADDR_[R|W]

Remove the use of IO_ADDR_[R|W] in the fsmc_nand driver. Instead, use a
pointer to the control registers to avoid doing several arithmetic
operations (including a multiplication) each time a control register is
read or written.

All references to IO_ADDR_[R|W] are not entirely removed from the driver
as, at this time, these values are needed by the NAND core in the
default ->read/write_byte/word() hooks. These references will be
entirely removed when switching to ->exec_op(), that does not make use
of these hooks anymore.

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