spapr_vio: Introduce a liobn number generating macros

spapr_vio: Introduce a liobn number generating macros

This introduces a macro which makes up a LIOBN from fixed prefix and
VIO device address (@reg property).

This is to keep LIOBN macros rendering consistent - the same macro for
PCI has been added by the previous patch.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>