drm/amdgpu: fix moved list handling in the VM

Only move BOs to the moved/relocated list when they aren't already on a list.

This prevents accidential removal from the evicted list.

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