drm/amdgpu: wait for IB test on first device open

Instead of delaying that to the first query. Otherwise we could try to use the
SDMA for VM updates before the IB tests are done.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Chunming Zhou <david1.zhou@amd.com>
Reviewed-by: Junwei Zhang <Jerry.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>