arm64: bus: unhide bus_space definition with sanitizers included

We'll only be redefining the various bus_* macros, not the definition of
struct bus_space.

Reviewed by: andrew
Sponsored by: Juniper Networks, Inc.
Sponsored by: Klara, Inc.

(cherry picked from commit c5500a01c78a47dfa9004d97a24a5f03bcfa1f75)