Update virtio-loopback module and adapter - priority feature

Update virtio-loopback module and adapter - priority feature

Updates [v2]
Separate the license files for virtio-loopback module
and adapter projects.

Updates [v1]
Add priority support for virtio devices handled by
virtio-loopback architecture. The new feature enables
virtio-loopback to prioritize requests (notification
and interrupts) coming from different virtio devices
based on a Round Robin scheduling algorithm and groups.

Bug-AGL: SPEC-4966

Change-Id: I5fbac8eebeccecd13968b03087e90540ee0d4615
Signed-off-by: Timos Ampelikiotis <t.ampelikiotis@virtualopensystems.com>