ASoC: msm8x10: Add the widget for secondary analog mic

AMIC3 is used as secondary analog mic in some use case
to service as stereo recording. Add the widget for the
secondary mic in machine driver to support this usage.

Change-Id: I91b13d43fc1c955d7c369ca5250d2c005b8a1935
Signed-off-by: Kuirong Wang <kuirongw@codeaurora.org>