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.

This patch fixes the issue that "No USB menu pops up when connect
the device to PC".

CRs-Fixed: 760672
(cherry-picked from commit c6c4bec1)

Change-Id: I3e8a62a290fd0b1867954cea00dced672524ac35