I tried 2 linux distributions aimed at retrogaming.
Lakka is based on librelec, it use nouveau driver with kms, but don't display anything on my hdmi TV or a pc monitor.
I also tried Recalbox, it's based on buildroot and the problem is exactly the same.
You can find all the logs here:
Can you try a newer kernel? There was an issue affecting MCP77/79 HDMI outputs that was fixed in 4.10 (commit 7dfee6827780d4228148263545af936d0cae8930 upstream).
I don't know how to update kernel in lakka/librelec, but I'll wait for a new version and I will test that. Thank you!