ASoC: msm: qdsp6: Sidetone is not supported for RT Proxy ports.

-During Voice call, when routed to RT Proxy Ports sidetone is
observed with delay and high volume.
-As per DSP limitation,by design it has high latencies for
RT Ports and sidetone specs will not be met.
-Disable sidetone from apps side by default for Voice call
on RT Proxy ports.

Change-Id: I28aaf3c7455cacba52ba1052c09cfe71c7323e94
CRs-Fixed: 313902
Signed-off-by: Laxminath Kasam <lkasam@codeaurora.org>