[PATCH] ppc64: move iSeries vio iommu init

Since the iSeries vio iommu tables cannot be used until after the vio bus has
been initialised, move the initialisation of the tables to there.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>