arm64: Implement bus_get_resource and bus_delete_resource.

These devmethods were not defined, leading to the surprising result
of using bus_set_resource(), and then immediately turning around
and getting zeros back from bus_get_resource(). These are now
simply passed through to the generic definitions, since there
is no need for them to be arm64 specific.

Note that jhb plans to replace most of the devmethods with
the generic versions.

Suggested by: jhb
Sponsored by: Netflix