pseries: Convert sPAPR TCEs to use generic IOMMU infrastructure

The pseries platform already contains an IOMMU implementation, since it is
essential for the platform's paravirtualized VIO devices.  This IOMMU
support is currently built into the implementation of the VIO "bus" and
the various VIO devices.

This patch converts this code to make use of the new common IOMMU
infrastructure.

We don't yet handle synchronization of map/unmap callbacks vs. invalidations,
this will require some complex interaction with the kernel and is not a
major concern at this stage.

Cc: Alex Graf <agraf@suse.de>

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
