nand: mxs_nand: make imx8mm can use hardware BCH and randomizer

imx8mm needs to BCH encode and set NAND page number needed to be
randomized

modify conditional compilation

Use CONFIG_IMX8M, so it apply to imx8mq/mm/mn

Signed-off-by: Alice Guo <alice.guo@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>