We need to make sure that no one else is using this in the
enable function and also that the work item hasn't raced
with the disabled function.

v2: Improve bisectability by moving one hunk to an earlier patch.

v3: added missing dev_priv declaration (Rodrigo)
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> (v2)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>