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GPU enumeration is bound to the current X -display.
The X- display is determined by the environment variable "DISPLAY" and for compute purpose can be overridden with the environment variable "COMPUTE" .
Make sure the "COMPUTE" environment variable points the the AMD X display.
export COMPUTE=:0 or export COMPUTE=:1 .
The problem was somewhere else. I though that I could use the integrated graphics and the GPU at the same time unfortunately the chipset does not support this.
Once I found that out I followed the instruction in this post  in combination with the knowledge base article "Application Note - Running ATI Stream Applications Remotely"  and now it even works over ssh.