virtio-pci: Introduce admin command sending function

Add support for sending admin command through admin virtqueue interface.
Abort any inflight admin commands once device reset completes. Activate
admin queue when device becomes ready; deactivate on device reset.

To comply to the below specification statement [1], the admin virtqueue
is activated for upper layer users only after setting DRIVER_OK status.

[1] The driver MUST NOT send any buffer available notifications to the
device before setting DRIVER_OK.

Signed-off-by: Feng Liu <feliu@nvidia.com>
Reviewed-by: Parav Pandit <parav@nvidia.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
Link: https://lore.kernel.org/r/20231219093247.170936-4-yishaih@nvidia.com


Signed-off-by: Alex Williamson <alex.williamson@redhat.com>