Let RemoteControlDisplay know more about playback position

The BT stack needs to differentiate between applications that use
 the new RemoteControlClient APIs to pass a playback position but
 don't have one yet, and applications that use the legacy API and
 will never pass a position.

Bug 9294855

Change-Id: I05cba82a073e6e0aaea1d8bbf9cc8c99da715f58