ab8500-bm: Flush all work queues before suspending

Flush all workqueues at suspend time to avoid suspending during work.

Signed-off-by: Jonas Aaberg <jonas.aberg@stericsson.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Marcus COOPER <marcus.xm.cooper@stericsson.com>