drm/amdgpu: Fix warning in dma_fence_is_later on resume from S3.

Problem:
amdgpu_ttm_set_buffer_funcs_status destroys adev->mman.entity on suspend
without releasing adev->mman.bdev.man[TTM_PL_VRAM].move fence
so on resume the new drm_sched_entity.fence_context causes
the warning against the old fence context which is different.

Fix:
When destroying sched_entity in amdgpu_ttm_set_buffer_funcs_status
release  man->move and set the pointer to NULL.

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