UMS: Add the missing notification when USB connected

The default USB functions not fall into any of the conditions,
cause "USB computer connection" missing.

Add the bool resource "always_popup_usb_computer_connection", use
it to control whether "USB computer connection" option appear.

CRs-Fixed: 676561

Change-Id: I14ae3abbc8e327303777f085b9750b406e0aa456