simplify the mdev interface v6

[Christoph Hellwig]

On Mon, Jul 18, 2022 at 10:01:40PM -0400, Eric Farman wrote:
> I'll get the problem with struct subchannel [1] sorted out in the next
> couple of days. This series breaks vfio-ccw in its current form (see
> reply to patch 14), but even with that addressed the placement of all
> these other mdev structs needs to be handled differently.

Alex, any preference if I should just fix the number instances checking
with either an incremental patch or a resend, or wait for this ccw
rework?