mtd: nand: fsmc: use ->exec_op()

Remove the deprecated ->cmd_ctrl() implementation to use ->exec_op() in
the fsmc_nand driver.

Implement the ->select_chip() hook to avoid having to support the hack
from the core that send a NAND_CMD_NONE with NAND_NCE to signal a
deassertion of nCE.

Also get rid of the last references to ->IO_ADDR_[R|W] that are not used
anymore.

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