layers: Complete support for VK_KHR_Display ext

Fixed using display extension only crash.
Added vkGetDisplayPlaneCapabilitiesKHR.
Fixes, that unique objects works for display extension.

Change-Id: I66727a430b9d55bfa40fdddc884f40c91aa29f11
diff --git a/layers/object_tracker.h b/layers/object_tracker.h
index 729e613..bf548e4 100644
--- a/layers/object_tracker.h
+++ b/layers/object_tracker.h
@@ -81,6 +81,7 @@
     bool mir_enabled;
     bool android_enabled;
     bool win32_enabled;
+    bool display_enabled;
 };
 
 typedef std::unordered_map<uint64_t, OBJTRACK_NODE *> object_map_type;