drm/amdgpu: print warning and taint kernel if lockup timeout is disabled

Make sure that we notice this in error reports.

Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>