PCI: Make of_irq_parse_pci() static

Now that the DT PCI code is merged into drivers/pci, of_irq_parse_pci() can
be static.

Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Frank Rowand <frowand.list@gmail.com>