[POWERPC] cell: Generalize io-workarounds code

This splits cell io-workaround code into spider-pci dependent code and
a generic part, and also moves io-workarounds initialization into
cell_setup_phb.

Signed-off-by: Kou Ishizaki <kou.ishizaki@toshiba.co.jp>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/kernel/of_platform.c

@@ -275,6 +275,8 @@ static int __devinit of_pci_phb_probe(struct of_device *dev,
 
 	/* Scan the bus */
 	scan_phb(phb);
+	if (phb->bus == NULL)
+		return -ENXIO;
 
 	/* Claim resources. This might need some rework as well depending
 	 * wether we are doing probe-only or not, like assigning unassigned