ACPI: PCI: move struct acpi_prt_entry declaration out of public header file

The struct acpi_prt_entry is used only in pci_irq.c, so there's no
need for the declaration to be public.  This patch moves it into
pci_irq.c.

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Len Brown <len.brown@intel.com>