drm/amdgpu: drm/amdgpu: Handle IOMMU enabled case

Handle all DMA IOMMU group related dependencies before the
group is removed and we try to access it after free.

v2:
Move the actul handling function to TTM

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>