libpayload: Implement usb_exit

So far it was empty and never published. It now exists and shuts down
all controllers (esp. EHCI which resets the port routers).

Change-Id: I81e355e8a05778d6397675417b085a094a6f48ee
Signed-off-by: Patrick Georgi <patrick.georgi@secunet.com>
Reviewed-on: http://review.coreboot.org/397
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

payloads/libpayload/drivers/usb/usb.c

@@ -67,6 +67,22 @@ detach_controller (hci_t *controller)
 	}
 }
 
+/**
+ * Shut down all controllers
+ */
+int
+usb_exit (void)
+{
+	if (usb_hcs == 0)
+		return 0;
+	hci_t *controller = usb_hcs;
+	while (controller != 0) {
+		controller->shutdown(controller);
+		controller = controller->next;
+	}
+	return 0;
+}
+
 /**
  * Polls all hubs on all USB controllers, to find out about device changes
  */

payloads/libpayload/drivers/usb/usbinit.c

@@ -139,8 +139,3 @@ usb_initialize (void)
 	return 0;
 }
 
-int
-usb_exit (void)
-{
-	return 0;
-}

payloads/libpayload/include/libpayload.h

@@ -123,6 +123,7 @@ void rtc_read_clock(struct tm *tm);
  * @{
  */
 int usb_initialize(void);
+int usb_exit (void);
 int usbhid_havechar(void);
 int usbhid_getchar(void);
 /** @} */