ASoC: msm: qdsp6v2: allow mic selection for multichannel ec

Allow MIC channel selection as the primary channel requested
by the application on Multichannel Echo Cancellation module.

CRs-fixed: 1102004
Change-Id: I94ba0f3171b4c7ebcc9936ca4f192f68de7be034
Signed-off-by: Rahul Sharma <sharah@codeaurora.org>
Signed-off-by: Derek Chen <chenche@codeaurora.org>