msi-map properties are used to tell an OS how PCI requester IDs are
mapped to ARM SMMU stream IDs.

for all PCI devices discovered in a system:
  -allocate a LUT (look-up-table) entry in that PCI controller
  -allocate a stream ID for the device
  -program and enable a LUT entry (maps PCI requester id to stream ID)
  -set the msi-map property on the controller reflecting the
   LUT mapping

basic bus scanning loop/logic was taken from drivers/pci/pci.c
pci_hose_scan_bus().

Signed-off-by: Stuart Yoder <stuart.yoder@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>