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

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

Change-Id: Idc92514874078c0f82ff22e07f4dde2238b74223