ACPICA: Windows compatibility: autoexecute root _INI method

Add support for execution of an _INI method at the namespace root.
Although not defined in the ACPI specification, this support was
added to Windows around the Vista timeframe. It is added here
for Windows compatibility.

Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lin Ming <ming.m.lin@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>