powerpc/pci: Cleanup some minor cruft

* Removed building setup-irq on ppc32, we don't use it anymore
* Remove duplicate prototype for setup_grackle() code that needs it
  gets it from <asm/grackle.h>
* Removed gratuitous pci_io_size type differences between ppc32/ppc64

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>