Now, compilation of util/dbus is implicit and depends
on libgio presence on the building host.
The patch adds options to manage libgio dependencies explicitly.

Signed-off-by: Denis Plotnikov <den-plotnikov@yandex-team.ru>
Message-Id: <20210312151440.405776-1-den-plotnikov@yandex-team.ru>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>