spapr_pci: Introduce a liobn number generating macros

spapr_pci: Introduce a liobn number generating macros

We are going to have multiple DMA windows per PHB and we want them to
migrate so we need a predictable way of assigning LIOBNs.

This introduces a macro which makes up a LIOBN from fixed prefix,
PHB index (unique PHB id) and window number.

This introduces a SPAPR_PCI_DMA_WINDOW_NUM() to know the window number
from LIOBN. It is used to distinguish the default 32bit windows from
dynamic windows and avoid picking default DMA window properties from
a wrong TCE table.

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>