ACPICA: Add support to externally execute _OSI method

The current implemenation of _OSI within ACPICA only allows other
control methods to execute _OSI. This change allows the host
OS to execute _OSI via the AcpiEvaluateObject interface. _OSI
is a special method -- it does not exist in the AML code, it is
implemented within ACPICA.

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>
diff --git a/drivers/acpi/parser/psparse.c b/drivers/acpi/parser/psparse.c
index dfd3d90..5156203 100644
--- a/drivers/acpi/parser/psparse.c
+++ b/drivers/acpi/parser/psparse.c
@@ -447,6 +447,10 @@
 			  walk_state, walk_state->parser_state.aml,
 			  walk_state->parser_state.aml_size));
 
+	if (!walk_state->parser_state.aml) {
+		return_ACPI_STATUS(AE_NULL_OBJECT);
+	}
+
 	/* Create and initialize a new thread state */
 
 	thread = acpi_ut_create_thread_state();