ASoC: msm: Disable gapless offload playback by default

Add a flag to platform private data to enable/disable gapless
playback. The platform data is updated by mixer control.
If gapless playback is disabled ignore next track and handle
partial drain as full drain. The stream is opened in gapless
mode based on the paltform data.

Change-Id: I36cea976bcb53f50069653aec4f0f8cc869f491a
Signed-off-by: Krishnankutty Kolathappilly <kkolat@codeaurora.org>