Here is the step-by-step to boot to U-Boot on RK3368-uQ7

Get the Source and build ATF
============================

  > git clone git://git.theobroma-systems.com/arm-trusted-firmware.git
  > cd arm-trusted-firmware
  > make CROSS_COMPILE=aarch64-linux-gnu- PLAT=rk3368 bl31
  > cp build/rk3368/release/bl31.bin ../u-boot/bl31-rk3368.bin

Configure U-Boot
================

  > cd ../u-boot
  > make lion-rk3368_defconfig

Build the TPL/SPL stage
=======================

  > make CROSS_COMPILE=aarch64-unknown-elf- ARCH=arm
  > tools/mkimage -n rk3368 -T rksd -d tpl/u-boot-tpl.bin spl-3368.img
  > cat spl/u-boot-spl-dtb.bin >> spl-3368.img

Build the full U-Boot and a FIT image including the ATF
=======================================================

  > make CROSS_COMPILE=aarch64-unknown-elf- ARCH=arm u-boot.itb

Write to a SD-card
==================

  > dd if=spl-3368.img of=/dev/sdb seek=64
  > dd if=u-boot.itb of=/dev/sdb seek=512


If everything went according to plan, you should see the following
output on UART0:

<debug_uart> U-Boot TPL board init
Trying to boot from BOOTROM
Returning to boot ROM...
Trying to boot from MMC1
NOTICE:  BL31: v1.3(release):v1.2-1320-gbf43a443
NOTICE:  BL31: Built : 18:04:47, Jul  5 2017


U-Boot 2017.07-00158-g2395e99858 (Jul 18 2017 - 21:03:31 +0200)

Model: Theobroma Systems RK3368-uQ7 SoM
DRAM:  2 GiB
MMC:   dwmmc@ff0c0000: 1, dwmmc@ff0f0000: 0
Using default environment

In:    serial@ff180000
Out:   serial@ff180000
Err:   serial@ff180000
Net:
Warning: ethernet@ff290000 (eth0) using random MAC address - d2:69:35:7e:d0:1e
eth0: ethernet@ff290000
Hit any key to stop autoboot:  2