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>
diff --git a/src/soc/intel/baytrail/southcluster.c b/src/soc/intel/baytrail/southcluster.c
index 365ac3d..26e0156 100644
--- a/src/soc/intel/baytrail/southcluster.c
+++ b/src/soc/intel/baytrail/southcluster.c
@@ -546,7 +546,7 @@
 	.enable_resources	= NULL,
 	.init			= sc_init,
 	.enable			= southcluster_enable_dev,
-	.scan_bus		= scan_static_bus,
+	.scan_bus		= scan_lpc_bus,
 	.ops_pci		= &soc_pci_ops,
 };