ACPICA: Update for "orphan" embedded controller _REG method support

This refers to _REG methods under the EC device that have no
corresponding operation region. This is allowed by the ACPI
specification. This update removes a dependency on having an
ECDT table, and will execute an orphan _REG method as long as
the handler for the EC is installed at the EC device node (not
the namespace root).  Rui Zhang (original update), Bob Moore
(update/integrate).

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Acked-by: Len Brown <len.brown@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>