First of all, great job @balbes150
Device: S905D 1GB RAM AP6255 WIFI + DVB T/S
I built with your tools and kernels an image with kernel 3.14, and kernel 5.2. Excellent work mate.
Mali GPU was not detected but now, using https://github.com/superna9999/meson_gx_mali_450/tree/DX910-SW-99002-r9p0-01rel0_meson_gx is ok
I've found https://github.com/Elyotna/linux/tree/5.2/v4l2-m2m-pr who is doing a great job developing v4l2 driver.
Using lsmod, I can see v4l2_m2m, meson_vdec... but when I use mpv to play any video is using CPU until 100%.