vfio: powerpc/spapr: Disable DMA mappings on disabled container

At the moment DMA map/unmap requests are handled irrespective to
the container's state. This allows the user space to pin memory which
it might not be allowed to pin.

This adds checks to MAP/UNMAP that the container is enabled, otherwise
-EPERM is returned.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
[aw: for the vfio related changes]
Acked-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>