ACPICA: Add signatures for undefined tables: ATKG, GSCI, IEIT

These ACPI tables have been seen in the field, but the actual
table definitions are unkown at this time.

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>

include/acpi/actbl2.h

@@ -79,6 +79,15 @@
 #define ACPI_SIG_WDAT           "WDAT"	/* Watchdog Action Table */
 #define ACPI_SIG_WDRT           "WDRT"	/* Watchdog Resource Table */
 
+#ifdef ACPI_UNDEFINED_TABLES
+/*
+ * These tables have been seen in the field, but no definition has been found
+ */
+#define ACPI_SIG_ATKG           "ATKG"
+#define ACPI_SIG_GSCI           "GSCI"	/* GMCH SCI table */
+#define ACPI_SIG_IEIT           "IEIT"
+#endif
+
 /*
  * All tables must be byte-packed to match the ACPI specification, since
  * the tables are provided by the system BIOS.