devicetree: Discriminate device ops scan_bus()

Use of scan_static_bus() and tree traversals is somewhat convoluted.
Start cleaning this up by assigning each path type with separate
static scan_bus() function.

For ME, SMBus and LPC paths a bus cannot expose bridges, as those would
add to the number of encountered PCI buses.

Change-Id: I8bb11450516faad4fa33b8f69bce5b9978ec75e5
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/8534
Tested-by: build bot (Jenkins)
Reviewed-by: Timothy Pearson <tpearson@raptorengineeringinc.com>

src/soc/intel/broadwell/smbus.c

@@ -94,7 +94,7 @@ static struct device_operations smbus_ops = {
 	.read_resources		= &smbus_read_resources,
 	.set_resources		= &pci_dev_set_resources,
 	.enable_resources	= &pci_dev_enable_resources,
-	.scan_bus		= &scan_static_bus,
+	.scan_bus		= &scan_smbus,
 	.init			= &pch_smbus_init,
 	.ops_smbus_bus		= &lops_smbus_bus,
 	.ops_pci		= &broadwell_pci_ops,