Merge tag 'u-boot-amlogic-20191018' of https://gitlab.denx.de/u-boot/custodians/u-boot-amlogic

- document alternative libretech-cc installation methods, including upstream TF-A and opensource tools
- add HDMI/CVBS display support for Amlogic G12A SoCs and SEI510 board
- add support for Amlogic A311D based Khadas VIM3
- add support for Amlogic S905X3 based SEI610 board, targeting Android support like SEI510