pci: layerscape: Fixup iommu-map for LS208xA

Commit 0aaa1a90 added support for LS208xA devices but fixing
iommu-map property is missing. This patch adds support for
fixing iommu-map.

Signed-off-by: Bharat Bhushan <Bharat.Bhushan@nxp.com>
Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
[YS: revised commit message]
Reviewed-by: York Sun <york.sun@nxp.com>