stagefright: Fix 24-bit WAV

 * When 24-bit output is enabled, we need to ensure that padding
   to 32 bits is done correctly.
 * Create new output buffers which conform to the correct format.

Change-Id: I5c07027ee8d3040147698c1f484b40991f943c03
Merge remote-tracking branch 'cm/cm-11.0' into cm-11.0