iommu: dma-mapping-fast: Store private data in domain->iova_cookie

Prepare for sharing iommu virtual address space between multiple devices
by moving private data out of 'struct device' and into the shared
iommu_domain.

Change-Id: I6e31307631fe29e0d8907244052086da7f8f3758
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>