ACPICA: Add string for _DDN method name.

The _DDN method will be used internally.
Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

include/acpi/acnames.h

@@ -52,6 +52,7 @@
 #define METHOD_NAME__CBA        "_CBA"
 #define METHOD_NAME__CID        "_CID"
 #define METHOD_NAME__CRS        "_CRS"
+#define METHOD_NAME__DDN        "_DDN"
 #define METHOD_NAME__HID        "_HID"
 #define METHOD_NAME__INI        "_INI"
 #define METHOD_NAME__PLD        "_PLD"