Add spec-compliant config.json files

xnnpack/config.json

@@ -12,7 +12,33 @@
       "file": "selfie_segmentation_xnnpack_fp32.pte",
       "precision": "fp32",
       "quantized": false,
-      "default": true
+      "default": true,
+      "methods": {
+        "forward": {
+          "inputs": [
+            {
+              "shape": [
+                1,
+                3,
+                256,
+                256
+              ],
+              "dtype": "float32"
+            }
+          ],
+          "outputs": [
+            {
+              "shape": [
+                1,
+                1,
+                256,
+                256
+              ],
+              "dtype": "float32"
+            }
+          ]
+        }
+      }
     }
   ]
 }