16-bit NAND is not supported on this chip using FCM. See the documentation for BRn[PS], which says that 16-bit is only supported for GPCM and UPM.
It should be possible to connect a 16-bit NAND chip via UPM, but this is not straightforward and you would not have any hardware ECC. It is recommended that you use an 8-bit NAND chip, and stick with FCM. Also note that the NAND chip must not have pages that are larger than 2048 bytes.