Finally got it! No kernel modifications needed, only v4l2-request.
Key notes:
Use bootlin code, latest master (not release-2019.03 tag)
I merged just one small patch from https://github.com/bootlin/libva-v4l2-request/pull/30/files (seems, it's unecessary)
Download kernel sources with corresponding version. For my armbian is: https://cdn.kernel.org/pub/linux/kernel/v5.x/linux-5.4.45.tar.xz
Extract 2 files from kernel/include/media mpeg2-ctrls.h and h264-ctrls.h and replace ones in v4l2-request
Replace V4L2_PIX_FMT_H264_SLICE_RAW to V4L2_PIX_FMT_H264_SLICE in v4l2-request source code
Compile and install (instruction is as 2 posts above)
Don't forget to set VLC as in https://linux-sunxi.org/Sunxi-Cedrus
Tested with VLC, usable with issues:
Artifacts in some videos h264 720p and higher, for example: https://imgur.com/nYFArT4 (360/480 works fine)
Scaling (fullscreen, resizing) not works, slowdown with message
[a310cb88] main filter error: Failed to create video converter
Minor issues in console output on playback (see bold)
Thanks to: @jernej for this post: