i9300: audio: force use both mics when back mic is selected

for video recording

Change-Id: Iaf8b878f7dc0a545ada41eab50962a945254c5f1
i9300: audio: increase mic gain

Change-Id: Ia54ed849ff54eae064717210065265e83a22595c
i9300: audio: always request stereo input

Change-Id: Id721c2727fb23340a0730746979843c6dfb41285
i9300: audio: fix capture period size and count

Change-Id: Ifca254e959f447a5794441ff0e6310a7f98e37c1