PCI: iproc: Make outbound mapping code more generic

Improve the iProc PCIe outbound mapping code by making it more generic and
removing redundant device tree properties 'brcm,pcie-ob-window-size' and
'brcm,pcie-ob-oarr-size'.  The driver is still backward compatible to
device tree binaries with the two properties specified.

The driver now automatically configures the correct mapping window size and
number of mapping windows based on the value of device tree property
'ranges' and the capability of of the iProc PCIe controller.

Signed-off-by: Oza Oza <oza.oza@broadcom.com>
Signed-off-by: Ray Jui <ray.jui@broadcom.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Scott Branden <scott.branden@broadcom.com>