mtd: rawnand: mxc: implement exec_op

This converts the driver to the more modern exec_op which gets us rid
of a bunch of legacy code. Tested on i.MX27 and i.MX25.

Signed-off-by: Sascha Hauer <[email protected]>
Signed-off-by: Miquel Raynal <[email protected]>
Link: https://lore.kernel.org/linux-mtd/20240522-mtd-nand-mxc-nand-exec-op-v4-2-75b611e0ac44@pengutronix.de

Author: saschahauer