PPC: e500: some pci related cleanup

- Use PCI_NUM_PINS rather than hardcoding
 - use "pin" wherever possible

Signed-off-by: Bharat Bhushan <Bharat.Bhushan@freescale.com>
Signed-off-by: Alexander Graf <agraf@suse.de>
PPC: e500: implement PCI INTx routing

This patch adds pci pin to irq_num routing callback.
This callback is called from pci_device_route_intx_to_irq to
find which pci device maps to which irq.
This fix is required for pci-device passthrough using vfio.

Also without this patch we gets below prints

"
  PCI: Bug - unimplemented PCI INTx routing (e500-pcihost)
  qemu-system-ppc64: PCI: Bug - unimplemented PCI INTx routing (e500-pcihost) "

and Legacy interrupt does not work with pci device passthrough.

Signed-off-by: Bharat Bhushan <Bharat.Bhushan@freescale.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Alexander Graf <agraf@suse.de>