Effects: add new effect volume flag

Add new effect flag to monitor requested volume from
audio framework.

Bug: 123251705
Test: on/off equalizer on spotify/google music
      switch songs with equalizer

Change-Id: Id89f6921923e7d55fa06c52579357fcd2f1c1fd0
Signed-off-by: Jasmine Cha <chajasmine@google.com>