ACPICA: Fail AcpiEnable if ACPI tables not loaded.

AcpiEnable will now fail if all of the required ACPI tables are not
loaded (FADT, FACS, DSDT). BZ 477

Signed-off-by: Alexey Starikovskiy <alexey.y.starikovskiy@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>
diff --git a/drivers/acpi/events/evxfevnt.c b/drivers/acpi/events/evxfevnt.c
index a3d148e..4eab4f5 100644
--- a/drivers/acpi/events/evxfevnt.c
+++ b/drivers/acpi/events/evxfevnt.c
@@ -65,6 +65,14 @@
 
 	ACPI_FUNCTION_TRACE(acpi_enable);
 
+	/* ACPI tables must be present */
+
+	if (!acpi_tb_tables_loaded()) {
+		return_ACPI_STATUS(AE_NO_ACPI_TABLES);
+	}
+
+	/* Check current mode */
+
 	if (acpi_hw_get_mode() == ACPI_SYS_MODE_ACPI) {
 		ACPI_DEBUG_PRINT((ACPI_DB_INIT,
 				  "System is already in ACPI mode\n"));