200823-01 - updated odroid u3/x2/x images and amlogic meson8 test image

• odroid x is now supported (did not work before in u-boot) - dtb and APPEND line in extlinux.conf need to be adjusted (see comment in the file)
• odroid u3 and odroid x2 are supported as before and maybe odroid u2 and odroid u might work as well with either the u3 or x dtb (not tested)
• the kernel is now at v5.4.58
• ubuntu focal build of my dev branch
  • ubuntu focal instead of bionic
  • uses a swapfile instead of a swap partition (for more flexibility and smaller images)
  • uses zswap to compress pages before swapping them out to reduce disk-io including zswap-stats.sh script to make visible how many disk writes are saved and how much memory is kind of gained
  • no more libreoffice installed by default (too big and not everyone really needs it out of the box)
  • uninstall snapd by default
• amlogic meson8 test image - no hdmi, v5.6.19 kernel, works on my mxq and my mx3 box, but cannot guarantee more yet :)