Before we had 2 layes of calls, one in the virtio ring layer and
another in the virtio-blk layer. There wasn't any reall need for that.
The change allows the virtio-vring code to call a callback that the virtio-blk
registers and execute it directly.

At the moment it's hard coded as queue '0' but further on it should be a function
of the device requirements. It is also possible to move it towards the device function
since this thread doesn't do anything other than wake up the driver worker.

Created abstract base classes for device and drivers, changed the flow of driver loading / device probing

host side reset calls

queue size correctly.

It was portion of BSD license and taken from Linux/uapi.
A matching license clause is under the license directory.