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/superio/smsc/lpc47b397/superio.c

@@ -134,7 +134,6 @@ static struct device_operations ops_hwm = {
 	.enable_resources = lpc47b397_pnp_enable_resources,
 	.enable           = pnp_alt_enable,
 	.init             = lpc47b397_init,
-	.scan_bus         = scan_static_bus,
 	.ops_smbus_bus    = &lops_smbus_bus,
 	.ops_pnp_mode     = &pnp_conf_mode_55_aa,
 };