Merge tag 'u-boot-rockchip-20191231' of https://gitlab.denx.de/u-boot/custodians/u-boot-rockchip

- Fix latest mainline kernel for rk3308
- Update rk3288-evb config to suport OP-TEE
- Fix for firefly-px30 DEBUG_UART channel and make it standalone
- Script make_fit_atf add python3 support
- Fix rk3328 timer with correct COUNTER_FREQUENCY
- Fix rk3328 ATF support with enable spl-fifo-mode