uboot-phytec

Merge tag 'rockchip-for-v2019.07' of https://gitlab.denx.de/u-boot/custodians/u-boot-rockchip

- rk3399 lpddr4 support
- rk3399-rock960 board support improvement
- Eliminate pyelftools dependency by make_fit_atf.py
- clean up rockchip dts to use -u-boot.dtsi
- use ARM arch/generic timer instead of rk_timer
- clean up Kconfig options for board support