buildroot/board/embest/riotboard/genimage.cfg

image sdcard.img {
    hdimage {
    }

    partition u-boot {
        in-partition-table = "no"
        image = "u-boot.imx"
        offset = 1024
    }

    partition rootfs {
        partition-type = 0x83
        image = "rootfs.ext2"
        offset = 1M
        size = 60M
    }
}