for pure fp16 (#37230)

Add pure fp16 support for fused transformer.

paddle/fluid/imperative/amp_auto_cast.cc

@@ -266,6 +266,13 @@ NameVarBaseMap CastPureFp16Inputs(const std::string& op_type,
         pair.first != "X") {
       continue;
     }
+    if ((op_type == "fused_attention" || op_type == "fused_feedforward")) {
+      if (pair.first == "LnScale" || pair.first == "LnBias" ||
+          pair.first == "Ln2Scale" || pair.first == "Ln2Bias" ||
+          pair.first == "Ln1Scale" || pair.first == "Ln1Bias") {
+        continue;
+      }
+    }
     VLOG(5) << "Op(" << op_type << "): Cast " << pair.first << " from "
             << GetDtypeStr(*pair.second.cbegin()) << " to "
             << framework::DataTypeToString(dst_type);