Ensure GeofenceHardware will return capabilities for old implementations.

New FLP HAL implementations will explicitly return their capabilities,
but old versions won't (the implicit capability in old versions was
GNNS).  Ensure that the getCapabilities feature of GeofenceHardware
will return GNNS for old binaries, so GmsCore doesn't have to worry
about versioning.

Change-Id: I4b1c942b0d68d87bfbb18b8c06fd9d8b8f68efa6