add arm64 to perf dimensions to override x86

Bug: b/346224942
Change-Id: I4e911461abba376d92af0fd5479fbbf3450f5895
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/354101
Commit-Queue: Christoffer Dewerin <jansson@webrtc.org>
Reviewed-by: Jeremy Leconte <jleconte@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#42457}

infra/specs/internal.client.webrtc.json

@@ -444,6 +444,7 @@
             }
           ],
           "dimensions": {
+            "cpu": "arm64",
             "device_status": "available",
             "id": "mac-438-e504",
             "os": "iOS-17.4.1",

infra/specs/mixins.pyl

@@ -18,6 +18,13 @@
       }
     }
   },
+  'arm64': {
+    'swarming': {
+      'dimensions': {
+        'cpu': 'arm64'
+      }
+    }
+  },
   'chrome-tester-service-account': {
     'swarming': {
       'service_account':

infra/specs/waterfalls.pyl

@@ -332,7 +332,7 @@
       },
       'iOS64 Perf': {
         'mixins': [
-          'ios-device-perf', 'webrtc-xctest', 'timeout-3h',
+          'arm64', 'ios-device-perf', 'webrtc-xctest', 'timeout-3h',
           'chrome-tester-service-account', 'xcode_15_main', 'mac_toolchain',
           'has_native_resultdb_integration', 'out_dir_arg'
         ],