Same concept as SeaGRUB, but for U-Boot. SeaBIOS starts, but
has a bootorder file loading U-Boot first, from flash.
You can interrupt it with the ESC menu, to boot something else
in SeaBIOS, including GRUB.
With this, we can effectively provide extremely user-friendly
UEFI-first setups in Libreboot.
Take that, edk2!
Signed-off-by: Leah Rowe <leah@libreboot.org>