powerpc/iommu: Remove dma_data union

To support "hybrid" DMA ops in a subsequent patch, we will need both
a direct DMA offset and an iommu pointer. Those are currently exclusive
(a union), so change them to be separate fields.

While there, also type iommu_table_base properly and make exist only
on CONFIG_PPC64 since it's not referenced on 32-bit at all.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --cc arch/powerpc/include/asm/device.h
Simple merge

diff --cc arch/powerpc/include/asm/dma-mapping.h
Simple merge

diff --cc arch/powerpc/include/asm/iommu.h
Simple merge