Add private permission for sending SMS via Messaging app

When the phone dialer sends an sms, it will use the Messaging app.
That way the sent messages will end up in the messaging provider db
and sending will be more reliable. Currently, the phone dialer
uses the SmsManager directly. For now, the feature is only
available to system apps and the permission is private. Bug 4563486

Change-Id: I10f7e1042683164ee61d01a2aaf738d19084da72