powerpc/iommu: Cleanup setting of DMA base/offset

Now that the table and the offset can co-exist, we no longer need
to flip/flop, we can just establish both once at boot time.

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