libpayload: Add a generic driver for usb hubs

The current drivers for external usb hubs and root hubs all follow
the same pattern. Before adding another one with 90% of the same code,
extract the common parts and rewrite them with a simple interface.

This also adds debouncing of new attachments. Current drivers just
waited 100ms before they reset the device. However, we should check
if the device becomes disconnected and reconnected during this period.

Porting of the current hub drivers will take place in separate
commits (when I have time to test the older HCIs).

Change-Id: I0c0ce0ac1b1cc51fb4cd009b3f9fcd1b9d2ba8fe
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: http://review.coreboot.org/3450
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

payloads/libpayload/Config.in

@@ -378,6 +378,10 @@ config USB_MSC
 	  storage devices (USB memory sticks, hard drives, CDROM/DVD drives)
 	  Say Y here unless you know exactly what you are doing.
 
+config USB_GEN_HUB
+	bool
+	default n
+
 endmenu
 
 menu "Debugging"