ACPI: thinkpad-acpi: keep track of module state

Keep track of module state (init, running, exit).  This makes it trivially
easy to avoid running any interrupt handlers, threads, or any other async
activity before we are ready, or when we want to go away.

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Len Brown <len.brown@intel.com>