ASoC: msm: support NULL topology for low latency playback

For the use case of audio playback such as touch tone which go
through low latency path no post processing are required to
reduce the latency. So, the topology in DSP should be selected
as NULL topology when open the ADM. Add support to select
NULL topology for low latency playback.

Change-Id: I76090058398a259d66f9fbe3df70ce34deb123b2
Signed-off-by: Subhash Chandra Bose Naripeddy <snariped@codeaurora.org>