Fixing AMDGPUs gang submit error handling

[Christian König]

Hi guys,

fives try to those patches. I think I finally manage to understand
how xarray works.

There are the high level and lower level API and we can actually save
tons of CPU cycles when we switch to the lower level API for adding
the fences to the xarray.

Looks like this is working now, but I won't mind some additional
testing or ideas for more test cases.

Regards,
Christian.