layers: Move dbg flag print to config header

The print function seems to go better here with the
config file parsing as they use similar values.
diff --git a/layers/layers_config.h b/layers/layers_config.h
index 7b608d7..3a232e2 100644
--- a/layers/layers_config.h
+++ b/layers/layers_config.h
@@ -34,6 +34,7 @@
 
 void setLayerOption(const char *_option, const char *_val);
 void setLayerOptionEnum(const char *_option, const char *_valEnum);
+void print_msg_flags(VkFlags msgFlags, char *msg_flags);
 #ifdef __cplusplus
 }
 #endif