drm/amdgpu: let amdgpu_vm_clear_bo figure out ats status v2

Instead of providing it from outside figure out the ats status in the
function itself from the data structures.

v2: simplify finding the right level
v3: partially revert changes from v2, more cleanup and split code
    into more functions.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Acked-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>