Change AudioTrack resampling buffers from 3 to 2

Move computation of minimum AudioTrack buffer size to server
for normal streaming PCM tracks.

Use server-side computation to exactly determine requirements
for the resampler to avoid triple buffering.

This reduces latency for normal audio tracks that require resampling,
and makes things consistent with the minimum buffer size.

Change-Id: I2f2ca0e599ee20e16559bc5c5dab61ed100da16c