pseries: Reset emulated PCI TCE tables on system reset

pseries: Reset emulated PCI TCE tables on system reset

The emulated PCI host bridge on the pseries machine incorporates an IOMMU
(PAPR TCE table).  Currently the mappings in this IOMMU are not cleared
when we reset the system.  This patch fixes this bug.  To do this it adds
a new reset function to the IOMMU emulation code.  The VIO devices already
reset their TCE tables, but they do so by destroying and re-creating their
DMA context.  This doesn't work for the PCI host bridge, because the
infrastructure for PCI IOMMUs has already copied/cached the DMA pointer
context into the subordinate PCI device structures.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>