[POWERPC] Remove iSeries_vio_dev

It was only being used to carry around dma_iommu_ops and vio_iommu_table
which we can use directly instead.  This also means that vio_bus_device
doesn't need to refer to them either.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Acked-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>