ASoC: msm: Add support for EC reference path

In order to use Eco Cancellation audio preprocessing effect on
audio capture path, EC reference should be available. Add a
kControl to set the EC reference path to support this feature.

Change-Id: Idbca32225469f8848cd0d5a5abc2c590210ee310
CRs-fixed: 482297

Signed-off-by: Ravi Kumar Alamanda <ralama@codeaurora.org>