nandbcb: support i.MX8M

Tested on i.MX8MM EVK, imx8mm evk uses BCH
encoding and randomizer
modify macro and print size_t with %zx
use CONFIG_IMX8M because it should apply to imx8mq/mm/mn

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