Thanks for the help, i finally found the solution.
It was really as simple as adding some kernel parameters to the append line in the extlinux.conf.
My looks now like this:
Code
LABEL LibreELEC
LINUX /KERNEL
FDT /sun50i-a64-pine64.dtb
APPEND boot=UUID=1304-1642 disk=UUID=fd58b039-6b5a-45b3-9576-325b932d81fa quiet console=ttyS0,115200 console=tty1 video=HDMI-A-1:3840x1080@30e
This topic can be closed, thank you again.