bus/driver: Make non-core interfaces unavailable on most object paths

bus/driver: Make non-core interfaces unavailable on most object paths

The o.fd.DBus interface needs to remain available on arbitrary object
paths for backwards compatibility, and the Introspectable interface
is genuinely useful, but everything else can be skipped.

This is arguably an incompatible change for the undocumented Verbose
interface, and for the GetAllMatchRules method on the undocumented
Stats interface: previously those were available at all object paths.

Reviewed-by: Philip Withnall <withnall@endlessm.com>
[smcv: Adjust comments, enum order, variable naming as per Philip's review]
Signed-off-by: Simon McVittie <smcv@collabora.com>
Bug: https://bugs.freedesktop.org/show_bug.cgi?id=101256