layers: Add parameter_validation namespace

Add parameter_validation namespace for utility functions.  Namespace will
be extended to include core layer functions in a future update.

Change-Id: I0929f5caacbf3e1b4509f051ea020566cce44e3e
diff --git a/layers/parameter_validation.cpp b/layers/parameter_validation.cpp
index 5bec9de..d1d09b6 100644
--- a/layers/parameter_validation.cpp
+++ b/layers/parameter_validation.cpp
@@ -46,6 +46,8 @@
 
 #include "parameter_validation.h"
 
+using namespace parameter_validation;
+
 struct layer_data {
     debug_report_data *report_data;
     std::vector<VkDebugReportCallbackEXT> logging_callback;