There is no need for delaying enqueuing ACPI tasks until the taskqueue's
threads have started. Taskqueues perfectly support that, as once
taskqueue threads are started, they will pick up enqueued tasks
naturally.
Remove this mechanism, which allows a number of simplifications:
- Remove the now-useless ACPI_TASK_ENQUEUED flag.
- Remove an atomic manipulation to set ACPI_TASK_ENQUEUED on each task enqueue in the common case.
- Simplify AcpiOsWaitEventsComplete() by using taskqueue_drain_all() directly, and make it print a warning when called before the taskqueue threads have started.
While here, use atomic functions to operate on 'acpi_taskq_started'.