Google has rolled out new update to the Google Play Music app which allows you to rate songs from the notification panel directly.
Google was preparing for this change from the past two updates. In the first, they changed some alignment of the icons and in the second, Google concise the album art in the notifications. Finally, they fixed two new icons to the notification tray of Google play Music.
You can sit tight and wait for the update to roll out to you, or you can grab the signed 18MB APK from the big orange button below.