powerpc/fsl-rio: add support for mapping inbound windows

Add support for mapping and unmapping of inbound rapidio windows.  This
allows for drivers to open up a part of local memory on the rapidio
network.  Also applications can use this and tranfer blocks of data
over the network.

Signed-off-by: Martijn de Gouw <martijn.de.gouw@prodrive-technologies.com>
[scottwood@freescale.com: updated commit message based on review]
Signed-off-by: Scott Wood <scottwood@freescale.com>