ANDROID: GKI: enable KMI enforcement

Add android/abi_gki_aarch64.stg as initial ABI representation of the
KMI, enable trimming of symbols outside KMI and start enforcing KMI.

While this is hard enforcement in the code base, we still allow
controlled changes to the ABI until KMI freeze.

Test: TH
Bug: 269323432
Change-Id: I016fe12aff4d781640340e16a2ae278e6bf5cd84
Signed-off-by: Aleksei Vetrov <vvvvvv@google.com>