Do calculations for item x out of y in AVRCP

We have to do this calculation ourself as sometimes the media player
doesn't give us the info and some carkits require it in order to display
the correct media metadata.

Bug: 78617730
Test: Use GPM and see that the track num shows up in the snoop logs
Change-Id: Iee4b20fd16163f0eeaac3f1fa0959f619ac194e6