drm/amdgpu: disable bulk moves for now

The changes to fix those are two invasive for backporting.

Just disable the feature in 4.20 and 5.0.

Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Cc: <stable@vger.kernel.org>    [4.20+]
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>