vdpa: add vdpa simulator for block device

stable inclusion
from stable-v5.13
commit 0c853c2c
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5WXCZ
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0c853c2c2924464bd86537164ed18d5d953b4909



----------------------------------------------------------------------

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: Max Gurtovoy <mgurtovoy@nvidia.com>
[sgarzare: various cleanups/fixes]
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Link: https://lore.kernel.org/r/20210315163450.254396-12-sgarzare@redhat.com


Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Pengyuan Zhao <zhaopengyuan@hisilicon.com>