Hi @Astralix ,
in the meanwhile I was able to build the XF86 video driver for 2D and 3D acceleration follwing the instructions in this repo. It looks a bit strange, because the driver is developed in the unstable_devel branch and master hasn't been touched for a while plus it uses code from two other external repos. Nevertheless compilation worked out of the box (I followed the etnadrm path described at the bottom of the README file).
To enable the XF86 driver you have to add the following to the XF86 config:
With this I was able to get glmark2 and glxgears to show up and apparently both are running with hardware acceleration. For glmark2 I had to set "MESA_GL_VERSION_OVERRIDE=2.1", because the etnaviv mesa driver reported only 1.4 .
Also chromium reports support for hardware acceleration now. Please note that the chromium ubuntu armhf build by default uses the setting "enable-low-end-device-mode" which shows webpages and especially pictures in a distored way. To use standard rendering you have to override the default chromium flags (set in /etc/chromium-browser/default):