AudioRecord and HAL input stream must be 16-bit PCM only

Currently there are 16-bit PCM assumptions in several places for capture:
 - resampler API
 - mRsmpInBuffer and mRsmpOutBuffer
 - RecordThread::threadLoop upmix, downmix, and resampling
 - possibly other places

Until those assumptions are removed, this CL enforces 16-bit PCM in both
client and server at all places where a format is checked.

Change-Id: I08b0570bff626ad0d341804825a72c14e61b4233