USB: gadget: composite: Add userspace notifications for USB state changes

Add switch to notify current USB configuration.  This can be used to detect
USB connect and disconnect events.

Broadcast a change via the usb_composite class when a USB function is
enabled or disabled.

Rename usb_function.hidden to usb_function.disabled.

Signed-off-by: Mike Lockwood <lockwood@android.com>
diff --git a/drivers/usb/gadget/f_adb.c b/drivers/usb/gadget/f_adb.c
index 194c767..0d25276 100644
--- a/drivers/usb/gadget/f_adb.c
+++ b/drivers/usb/gadget/f_adb.c
@@ -613,7 +613,7 @@
 	dev->function.disable = adb_function_disable;
 
 	/* start disabled */
-	dev->function.hidden = 1;
+	dev->function.disabled = 1;
 
 	/* _adb_dev must be set before calling usb_gadget_register_driver */
 	_adb_dev = dev;