I have found several instructions on how to flash a new u-boot image it to the Quad SPI NOR flash on LS1021A-IOT.
Resources like this seem helpful.
However, my question is this: Is there an easy place to download the latest version of U-boot for LS1021A-IOT? I just want a U-boot version that supports SATA on the board. I don't want to rebuild it, or download a huge package, etc. I just want to get the latest .bin for the board that will setup the SATA for booting Linux from the SSD.