mtd: mxs_nand: Support EDO mode for imx8mn architecture

Add support for imx8mn architecture in order to run the NAND
in fast edo mode.

Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>
Reviewed-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>