Use megous fork of U-boot
Uses this fork under the hood: https://megous.com/git/u-boot/refs/?h=opi-v2020.01 Provides GPIO support and other stuff for the PinePhone in U-boot
Uses this fork under the hood: https://megous.com/git/u-boot/refs/?h=opi-v2020.01 Provides GPIO support and other stuff for the PinePhone in U-boot