ACPICA: Events: Reduce source code difference for the ACPI_EVENT_FLAG_HANDLE support.

ACPICA: Events: Reduce source code difference for the ACPI_EVENT_FLAG_HANDLE support.

This patch is a partial linuxized result of the following ACPICA commit:
  ACPICA commit: a73b66c6aa1846d055bb6390d9c9b9902f7d804d
  Subject: Add "has handler" flag to event/gpe status interfaces.
  This change adds a new flag, ACPI_EVENT_FLAGS_HAS_HANDLER to the
  acpi_get_event_status and acpi_get_gpe_status external interfaces. It
  is set if the event/gpe currently has a handler associated with it.
This commit back ports ACPI_EVENT_FLAG_HANDLE from Linux upstream to
ACPICA, the flag along with its support code currently can only be found
in the Linux upstream and is used by the ACPI sysfs GPE interfaces and
the ACPI bus scanning support.

Link: https://github.com/acpica/acpica/commit/a73b66c6
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>