Move media related hidden API flag file entries to frameworks/av

Bug: 179354495
Test: m com.android.media
      - ensure that the generated APEX is byte-for-byte identical
        before and after these changes.
      m out/soong/hiddenapi/hiddenapi-flags.csv
      - make sure that they are not changed by this.
Change-Id: I0dea4284723835c0592ce9aaf7382e344ae959f7