WIP: odroid-u3: new device

odroid-u3 running 5.4 kernel on Debian 10

The main goal of this merge request is to port odroid-u3 from HardKernel into postmarketOS, because Ubuntu 20.04 or Debian 10 may seem too much for the device in terms of RAM.

All the information I collected about the device is here:
https://www.hardkernel.com/shop/odroid-u3/

All the information about porting the device is here:
https://forum.odroid.com/viewtopic.php?t=9342
https://forum.odroid.com/viewtopic.php?f=55&t=3691&p=269246#p269246

HardKernel original sources (odroid-u3 is obsolete):
https://github.com/hardkernel/linux/tree/odroid-3.8.y

Kernel (patched) sources:
https://github.com/tobiasjakobi/linux-odroid-public/tree/odroid-5.4.y
https://github.com/tobiasjakobi/linux-odroid-public/tree/odroid-5.8.y

ImageBuilder for working Ubuntu 20.04 with the 5.4.58 kernel:
https://github.com/hexdump0815/imagebuilder

According to the author, hexdump0815, this imagebuilder from scratch could also run on other arm (based on Samsung exynos4412) devices, see https://github.com/hexdump0815/imagebuilder#system-specific-information.

• Kernel compiles
• dtbs well placed in my linux-odroid-u3 APKBUILD file and device-odroid-u3 APKBUILD file?
• u-boot is detected (blue light on odroid)
• Boots