Comment # 59 on bug 95306 from Jaime Rodrigo

Sadly it doesn't do any good. I get a blackout anyways. Tried it
(amdgpu.powerplay=0) also on RC5 (which, as I said before, works good) and it
makes it blackout. 

I believe the problem lies on Crossfire or something like that, since it makes
both cards run @100% all the time.