Merge tag 'u-boot-amlogic-20190731' of https://gitlab.denx.de/u-boot/custodians/u-boot-amlogic

- sync Amlogic G12A DT with linux 5.3-rc1
- add support for 4GiB DRAM memory
- add support for Amlogic G12B based Odroid-N2
- small duplicate logic fix for gxbb clock driver