drm/amdgpu: cleanup setting bulk_movable

We only need to set this to false now when BOs are removed from the LRU.

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