Update from original Marvell U-Boot to mainline U-Boot:
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Generate the U-Boot image with these commands:

$ make clearfog_defconfig
$ make

The resulting image including the SPL binary with the
full DDR setup is "u-boot-spl.kwb".

Now all you need to do is copy this image on a SD card.
For example with this command:

$ sudo dd if=u-boot-spl.kwb of=/dev/sdX bs=512 seek=1

Please use the correct device node for your setup instead
of "/dev/sdX" here!