Trigger talkback for notification volume change

Triggers talkback to say the content description of the title of
notification volume when notification volume is set to vibrate or silent
mode.

Fixes: 285453719
Fixes: 285455826
Test: manually checked when the ring volume is set to 0% and when the
notification volume is set to 0%. Check the video in the bug link.

Change-Id: I4bd65bdbfa41793fc8e32c295185363ca36cc0d7