simplify the mdev interface v8

[Christoph Hellwig]

On Wed, Sep 28, 2022 at 12:56:50PM -0600, Alex Williamson wrote:
> That fixes the crash, but available_instances isn't working:

I see the same behavior both with and without my series.  Given that
the code to report it didn't change that is also very much expected.

So something in i915 fails to update the resources when deleting
instances, but it is an existing issue.