drm/amdgpu: rework moved handling in the VM v2

Instead of using the vm_state use a separate flag to note
that the BO was moved.

v2: reorder patches to avoid temporary lockless access

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>