Player activity notification: SoundPool not ready for activity reporting

Some plumbing is missing to accurately report SoundPool's playback
   state, do not report it

Test: run cts -m CtsMediaTestCases -t android.media.cts.AudioPlaybackConfigurationTest
Bug: 35263297
Change-Id: I93389c87e5136912bfd11831b87d80495c3a1c3e