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/tests/xglrenderframework.h b/tests/xglrenderframework.h
index 00343a0..1c8da22 100644
--- a/tests/xglrenderframework.h
+++ b/tests/xglrenderframework.h
@@ -307,7 +307,7 @@
 
 };
 
-class XglDescriptorSetObj : public xgl_testing::DescriptorRegion
+class XglDescriptorSetObj : public xgl_testing::DescriptorPool
 {
 public:
     XglDescriptorSetObj(XglDevice *device);