[PATCH] powerpc: pseries: Use generic dma-window parsing function

Change the pseries iommu init code to use the new of_parse_dma_window()
to parse the ibm,dma-window and ibm,my-dma-window properties of pci and
virtual device nodes.

Also, clean up vio_build_iommu_table() a little.

Tested on pseries, with both vio and pci devices.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Acked-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Paul Mackerras <paulus@samba.org>