Migrate from old key when combining device and media data

Fixes: 160256461
Test: manual - Play Spotify. Dismiss app in overview. Open app in
launcher and select a cast device. Start playing again and check media
player in QS. Verify that a cast icon appears in upper right corner.

Change-Id: If830239f8753d35f3c4d9f3a234d00ee4d89a054