Audio: Add Alsa mixer control to enable loopback.

Audio: Add Alsa mixer control to enable loopback.

BZ: 27786

By default,Loopback was enabled,this was causing issue with simultaneous
playback and capture.

This patch added alsa mixer control to enable loopback when required.

Change-Id: I8609927802bf819076cce43c5345f6f16aa3fbbf
Signed-off-by: namarta <namartax.kohli@intel.com>
Reviewed-on: http://android.intel.com:8080/42118
Reviewed-by: Agarwal, Vaibhav <vaibhav.agarwal@intel.com>
Reviewed-by: Vinnakota, Lakshmi N <lakshmi.n.vinnakota@intel.com>
Reviewed-by: M, Arulselvan <arulselvan.m@intel.com>
Tested-by: M, Arulselvan <arulselvan.m@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>