Treat ATTEST_KEY keys as signing keys am: b5a5df3c6c am: f671b05ad8 am: 7ea3f49e6c am: 8d4d40d946

Original change: https://android-review.googlesource.com/c/platform/system/keymaster/+/1876198

Change-Id: Iffbb404e9125c8883e031dee478beb096678fc86