msm: camera: crm: Access the task list of workqueue with locks

Add locks at proper place while acquiring, enqueuing and executing
a task from the list and while accessing the elements of workq.
Also the change ensures that the workq is destroyed safely.

Change-Id: I01bf2032133cc1a5269d699b94770141347d3cd0
Signed-off-by: Abhilash Kumar <krabhi@codeaurora.org>
Signed-off-by: Karthik Anantha Ram <kartanan@codeaurora.org>