Release page table DMA buffer when the IOMMU domain is not used:
- Domain freed.
- IOMMU is attaching to a new domain.
Since one sprd IOMMU servers only one client device, if the IOMMU has
been attached to other domain, it has to be detached first, that's
saying the DMA buffer should be released, otherwise that would
cause memory leak issue.
Signed-off-by: Chunyan Zhang<chunyan.zhang@xxxxxxxxxx>