It appears as thought the SDP has gone through some significant changes since the MX25. If I remember correctly, I would send a few magic commands, the DCD, and eventually an application image, that would be burned directly to NAND flash.
I am now targeting custom i.MX6ULL and i.MX7dual targets. After reviewing the current mfgtool, it seems that U-Boot is the preferred mechanism to dd the image to non-volatile storage. I wonder if this is only an effort to keep the mfgtool target agnostic. And if so, it stands to wonder whether the old capabilities still exist. This is a long winded way of getting to my question: do either of these targets have the ability to write to SPI NOR flash without any extra software? Please clarify for both targets if it's not too much trouble.