Introduce a new flag showing whether the event has an event handler/method.

For all the GPEs and Fixed Events,
 1. ACPI_EVENT_FLAG_HANDLE is cleared, it's an "invalid" ACPI event.
 2. Both ACPI_EVENT_FLAG_HANDLE and ACPI_EVENT_FLAG_DISABLE are set,
    it's "disabled".
 3. Both ACPI_EVENT_FLAG_HANDLE and ACPI_EVENT_FLAG_ENABLE are set,
    it's "enabled".
 4. Both ACPI_EVENT_FLAG_HANDLE and ACPI_EVENT_FLAG_WAKE_ENABLE are set,
    it's "wake_enabled".

Among other things, this prevents incorrect reporting of ACPI events
as being "invalid" when it's really just (temporarily) "disabled".
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Len Brown <len.brown@intel.com>