Ship Hardware Platform Extension API in Stable

Bug: 860311
Change-Id: I64a96abec0161200fb55f78c5492e20970fa9c3b
Reviewed-on: https://chromium-review.googlesource.com/c/1333369Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Commit-Queue: Guido Urdaneta <guidou@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607603}

chrome/common/extensions/api/_permission_features.json

@@ -283,7 +283,7 @@
     "location": "policy"
   },
   "enterprise.hardwarePlatform": {
-    "channel": "beta",
+    "channel": "stable",
     "extension_types": ["extension"],
     "location": "policy"
   },