A2DP: Based on the AAC parameters to calculate its encoder interval

When running AAC software encoder, the PCM data size per AAC frame is:
  1024 (sample counts per frame) * 2 (16 bits per sample) * 2 (stereo)
If we are using 44.1 kHz, the interval is about 23.22 ms. When using 48
kHz, it is about 21.33 ms. Here we determine the interval based on the
codec configuration and feeding parameters while updating the AAC
encoder.

Bug: 146399686
Test: There were AAC frames every 23 ms in BTSnoop
Change-Id: I8af7696917b007cb751a8991f21b344724b9ba94