fdt: Added helper to set PCI dma-ranges property

Added fdt_pci_dma_ranges() that parses the pci_region info from the
struct pci_controller and populates the dma-ranges based on it.

The max # of windws/dma-ranges we support is 3 since on embedded
PowerPC based systems this is the max number of windows.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Andrew Fleming-AFLEMING <afleming@freescale.com>