We have both IRQ sinks and GPIO inputs. These are in principle exactly
the same thing, so remove the former.
Signed-off-by: Paul Brook <paul@codesourcery.com>
Implement and use a common device bus state. The main side-effect is
that creating a bus and attaching it to a parent device are no longer
separate operations. For legacy code we allow a NULL parent, but that
should go away eventually.
Also tweak creation code to veriry theat a device in on the right bus.
Signed-off-by: Paul Brook <paul@codesourcery.com>
