layers:  Add GetPhysicalDeviceExtInfo to DrawState

Allows DrawState to be enabled in layers_validation_test
diff --git a/tests/layer_validation_tests.cpp b/tests/layer_validation_tests.cpp
index 42a3b20..688bb71 100644
--- a/tests/layer_validation_tests.cpp
+++ b/tests/layer_validation_tests.cpp
@@ -158,6 +158,7 @@
         instance_extension_names.push_back("Threading");
 
         device_extension_names.push_back("MemTracker");
+        device_extension_names.push_back("DrawState");
         device_extension_names.push_back("ObjectTracker");
         device_extension_names.push_back("Threading");