frameworks/av: Support 24 bit pcm data conversion to 8_24 format

-To play 24 bit pcm on offload path, WAV extractor must convert the
input into 8_24 bit format. Currently, 24 bit data is converted to
16 bit samples only. By padding first byte to zero, 24 bit data is
converted to 8_24 format.
-By setting an output format key in Awesome player, WAV extractor
knows whether to provide data in 16 bit or 8_24 bit format.

Change-Id: I4fcdfcf4a9be8a1bb54ccd39735e8d570f90b658