spapr_pci: Allow VFIO devices to work on the normal PCI host bridge

spapr_pci: Allow VFIO devices to work on the normal PCI host bridge

The core VFIO infrastructure more or less allows VFIO devices to work
on any normal guest PCI host bridge (PHB) without extra logic.
However, the "spapr-pci-host-bridge" device (as opposed to the special
"spapr-pci-vfio-host-bridge" device) breaks this by using a partially
KVM accelerated implementation of the guest kernel IOMMU which won't
work with VFIO devices, without additional kernel support.

This patch allows VFIO devices to work on the spapr-pci-host-bridge,
by having it switch off KVM TCE acceleration when a VFIO device is
added to the PHB (either on startup, or by hotplug).

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Laurent Vivier <lvivier@redhat.com>