ASoC: Add support for DSP based DTMF detection

Enable DTMF tone detection in voice call's RX path using DSP.
Update DTMF platform driver to add support for capture stream
through which dtmf tone detection information will be passed
to the user space.

Change-Id: Ib1c2fb06bae2f03ae760791a0fbec574be7656be
Signed-off-by: Shiv Maliyappanahalli <smaliyap@codeaurora.org>