A2DP-related naming refactoring and cleanup

* Renamed A2DP-related function names, types, constants and fields.
  Also, move some of those functions to a better location.
 - tAVDT_DATA_CBACK -> tAVDT_SINK_DATA_CBACK
 - tAVDT_MEDIA_CBACK -> tAVDT_SINK_MEDIA_CBACK
 - p_data_cback -> p_sink_data_cback
 - p_media_cback -> p_sink_media_cback
 - p_app_data_cback -> p_app_sink_data_cback
 - tBTA_AV_DATA_CBACK -> tBTA_AV_SINK_DATA_CBACK
 - BTA_AV_MEDIA_SINK_CFG_EVT -> BTA_AV_SINK_MEDIA_CFG_EVT
 - BTA_AV_MEDIA_DATA_EVT -> BTA_AV_SINK_MEDIA_DATA_EVT
 - bta_av_stream_data_cback() -> bta_av_sink_data_cback()
 - bte_av_media_callback() -> bte_av_sink_media_callback()
 - tBTA_AV_CODEC -> tA2D_CODEC
 - btif_a2dp_get_track_frequency() -> A2D_sbc_get_track_frequency()
 - btif_a2dp_get_track_channel_count() -> A2D_sbc_get_track_channel_count()
 - dump_codec_info() -> A2D_sbc_dump_codec_info()

* Misc. other cleanup:
  - log messages cleanup
  - normalize usage of "+=" in Android.mk files

Change-Id: Ida1528fb5d75cc322533f921daefb65be44562f1