Add Dual Transfer Mode support

This change includes the following to support DTM:
(1) For GSM, decode the "concurrent services support indicator" field
from RIL_REQUEST_VOICE_REGISTRATION_STATE request and based on the
value of this CSSI field allow concurrent CS and PS services to
applications.

(2) Notify data connection changed on CSS indicator update.

(3) When the phone moves from a DTM cell to a non DTM cell while in
active voice call, data connection is not suspended. To fix this,
consider CSS indicator change also for notifying data connection.

(4) To determine concurrent voice and data support, it is necessary to
query Data Radio Tech.

Test: with modified RIL to return desired css indicator
Test: Passed new unit test
Bug: 21079150

Change-Id: I57c445ee28be4e1c0f2934cb136a70d39447511c