This will allow running vDPA for virtio block protocol.

It's a preliminary implementation with a simple request handling:
for each request, only the status (last byte) is set.
It's always set to VIRTIO_BLK_S_OK.

Also input validation is missing and will be added in the next commits.
Signed-off-by: NMax Gurtovoy <mgurtovoy@nvidia.com>
[sgarzare: various cleanups/fixes]
Acked-by: NJason Wang <jasowang@redhat.com>
Signed-off-by: NStefano Garzarella <sgarzare@redhat.com>
Link: https://lore.kernel.org/r/20210315163450.254396-12-sgarzare@redhat.comSigned-off-by: NMichael S. Tsirkin <mst@redhat.com>