Strange GPU detection/hread number and crash in 2.8.6
Hello everyone,

I was using a RX570 XFX to mine with the graft with XMrig 2.8.6 and I was around 580h/s.

Then I have add a RX560 and there are 2 things strange:

-Firstly XMrig tells me that I have 2 RX560 (but just the name, it gives to them different intensities...)
![image](https://user-images.githubusercontent.com/45048747/48859542-9853d480-edbe-11e8-9258-65915f45f7ca.png)

-Secondly it creates 2 thread by card, I say why not, it s faster. But why does he chosen that now? Why hasn t it do that with only my RX570?
![image](https://user-images.githubusercontent.com/45048747/48859677-07c9c400-edbf-11e8-90c8-ff8404b6b95b.png)


It's not really issues but mainly questions.

Thanks for your help.

