[POWERPC] Fix compile problem without CONFIG_PCI

Compile fails without defining CONFIG_PCI.
The patch fix this.

[paulus@samba.org: Moved of_irq_pci_swizzle so we only need one #ifdef]

Signed-off-by: Li Yang <leoli@freescale.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>