asoc: add support to set custom channel mixer coefficients

Enhance Channel Mixer control for MultiMedia Frontends to
get custom channel mixer coefficients from userspace and
use it during device routings to control stream to device
channel mappings.

Change-Id: Icf950377dede46b097c8656174af5eb311bf719a
Signed-off-by: Cong Tang <congt@codeaurora.org>
Signed-off-by: Dhananjay Kumar <dhakumar@codeaurora.org>