drm/amdgpu: drop bo_list_clone when no scheduler

bo_list_clone() will take a lot of time when bo_list hold too much
elements, like above 7000

Signed-off-by: Monk.Liu <monk.liu@amd.com>
Reviewed-by: Chunming Zhou <david1.zhou@amd.com>
Reviewed-by: Jammy Zhou <jammy.zhou@amd.com>