configs: Add Speaker mixer controls for RAS test device

For tuning the Receiver Aided Stereo(RAS), add speaker mixer
controls for RAS test device  for 8998. This is required for
offline RAS module tuning. Also change mixer control file name
from aanc_xxx.txt to audio_xxx.txt as this file not only used
for aanc anymore.

Change-Id: I1b937020793c7c0909e4e5265afc62224fde97e7