adjust backend priority, GPUDNN>GPU>ONEDNN>CPU

paddle/phi/common/backend.h

@@ -42,18 +42,20 @@ enum class Backend : uint8_t {
 
   // basic kernel backend
   CPU,
+  // the third library backend
+  ONEDNN,
 
-  // various acceleration devices' backends
+  // acceleration device's backend
   GPU,
+  // the third library backend
+  GPUDNN,  // cuDNN and hipDNN
+
+  // various acceleration devices' backends
   XPU,  // XPU currently does not exist at the same time as CUDA
   NPU,  // NPU currently does not exist at the same time as CUDA
   MLU,  // MLU currently does not exist at the same time as CUDA
   IPU,
 
-  // the third library backend
-  ONEDNN,
-  GPUDNN,  // cuDNN and hipDNN
-
   // paddle kernel primitives backend
   KPS,