pseries: Convert VIO code to QOM style type safe(ish) casts

pseries: Convert VIO code to QOM style type safe(ish) casts

Curerntly the pseries VIO device code contains quite a few explicit
uses of DO_UPCAST and plain C casts.  This is (obviously) type unsafe,
and not the conventional way of doing things in the QOM model.  This
patch converts the code to use the QOM convention of per-type macros
to do verified casts with OBJECT_CHECK().

Signed-off-by: David Gibson <[email protected]>
Signed-off-by: Alexander Graf <[email protected]>