binding: rename descriptor region to descriptor pool

This should be trivial, except that the intel driver has intel_desc_pool
internally.  Exchange the names of intel_desc_pool and intel_desc_region.
diff --git a/include/xglLayer.h b/include/xglLayer.h
index 5a25ca0..3b7624d 100644
--- a/include/xglLayer.h
+++ b/include/xglLayer.h
@@ -86,10 +86,10 @@
     xglLoadPipelineDerivativeType LoadPipelineDerivative;
     xglCreateSamplerType CreateSampler;
     xglCreateDescriptorSetLayoutType CreateDescriptorSetLayout;
-    xglBeginDescriptorRegionUpdateType BeginDescriptorRegionUpdate;
-    xglEndDescriptorRegionUpdateType EndDescriptorRegionUpdate;
-    xglCreateDescriptorRegionType CreateDescriptorRegion;
-    xglClearDescriptorRegionType ClearDescriptorRegion;
+    xglBeginDescriptorPoolUpdateType BeginDescriptorPoolUpdate;
+    xglEndDescriptorPoolUpdateType EndDescriptorPoolUpdate;
+    xglCreateDescriptorPoolType CreateDescriptorPool;
+    xglClearDescriptorPoolType ClearDescriptorPool;
     xglAllocDescriptorSetsType AllocDescriptorSets;
     xglClearDescriptorSetsType ClearDescriptorSets;
     xglUpdateDescriptorsType UpdateDescriptors;