See the original sdboot declaration here. Note that the above commands are loading the uImage and dtb from on-board eMMC. The MMC device parameter can be changed to load kernel uImage and dtb from SD card.
As Sanchayan mentions, our U-Boot already has a sdboot deceleration. I would recommend to make use of it. Prepare a SD-card with two partition, the first being a FAT partition and containing the kernel (uImage) and the device tree (imx6dl-colibri-eval-v3.dtb). The second is the root file system, use a ext3 file system and copy the content of your rootfs (using something like this: sudo cp -pPr rootfs/* /run/media/ags/RFS).
Make sure to use the default environment using env default -a. With that SD card, and the default environment, it should work just by using run sdboot.
It would be nice if you could update the knowledge base entry “Linux - Booting | Toradex Developer Center” and insert the information about how the partitions have to be formatted by now for i.MX6 because it differs from the one-Partition-solution described there that peio first tried (and today the same happened to me).