spapr_iommu: Realloc guest visible TCE table when hot(un)plugging vfio-pci

spapr_iommu: Realloc guest visible TCE table when hot(un)plugging vfio-pci

This replaces g_malloc() with spapr_tce_alloc_table() as this is
the standard way of allocating tables and this allows moving the table
back to KVM when unplugging a VFIO PCI device and VFIO TCE acceleration
support is not present in the KVM.

Although spapr_tce_alloc_table() is expected to fail with EBUSY
if called when previous fd is not closed yet, in practice we will not
see it because cap_spapr_vfio is false at the moment.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>