ASoC: msm: qdsp6v2: Add mutex to ensure atomicity

Make sure that afe command sent to DSP is atomic in nature
and doesn't get overwritten in concurrent scenarios.

Change-Id: I86558c293f0ce5d78533b79ed13a23e52e367c1d
Signed-off-by: Anish Kumar <kanish@codeaurora.org>