Add reserved parameter to xglEnumerateLayers for layer usage

This parameter can be used by layer for getting GPA and gpu info queries.
Also add xglEnumerateLayers() to Basic layer, to show example of only
supporting a particular GPU.
diff --git a/layers/draw_state.c b/layers/draw_state.c
index d5b8f19..4679850 100644
--- a/layers/draw_state.c
+++ b/layers/draw_state.c
@@ -927,14 +927,14 @@
     return result;
 }
 
-XGL_LAYER_EXPORT XGL_RESULT XGLAPI xglEnumerateLayers(XGL_PHYSICAL_GPU gpu, XGL_SIZE maxLayerCount, XGL_SIZE maxStringSize, XGL_CHAR* const* pOutLayers, XGL_SIZE * pOutLayerCount)
+XGL_LAYER_EXPORT XGL_RESULT XGLAPI xglEnumerateLayers(XGL_PHYSICAL_GPU gpu, XGL_SIZE maxLayerCount, XGL_SIZE maxStringSize, XGL_CHAR* const* pOutLayers, XGL_SIZE * pOutLayerCount, XGL_VOID* pReserved)
 {
     if (gpu != NULL)
     {
         XGL_BASE_LAYER_OBJECT* gpuw = (XGL_BASE_LAYER_OBJECT *) gpu;
         pCurObj = gpuw;
         pthread_once(&tabOnce, initLayerTable);
-        XGL_RESULT result = nextTable.EnumerateLayers((XGL_PHYSICAL_GPU)gpuw->nextObject, maxLayerCount, maxStringSize, pOutLayers, pOutLayerCount);
+        XGL_RESULT result = nextTable.EnumerateLayers((XGL_PHYSICAL_GPU)gpuw->nextObject, maxLayerCount, maxStringSize, pOutLayers, pOutLayerCount, pReserved);
         return result;
     } else
     {