vdpa/mlx5: fix queue update synchronization

vdpa/mlx5: fix queue update synchronization

The driver CQ event management is done by non vhost library thread,
either the dpdk host thread or the internal vDPA driver thread.

When a queue is updated the CQ may be destroyed and created by the vhost
library thread via the queue state operation.

When the queue update feature was added, it didn't synchronize the CQ
management to the queue update what may cause invalid memory access.

Add the aforementioned synchronization by a new per device configuration
mutex.

Fixes: c47d6e83334e ("vdpa/mlx5: support queue update")

Signed-off-by: Xueming Li <xuemingl@mellanox.com>
Acked-by: Matan Azrad <matan@mellanox.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>