drm/amdgpu: replace fence pointer with fence data in traces

Fence data is easier to read and allows us to correlate to identify
corresponding dma_fence ftrace events.

Reviewed-by: Chunming Zhou <david1.zhou@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Andres Rodriguez <andresx7@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>