Merge shared code that's necessary for mlx5 vdpa bits to build.

The branch itself includes a small number of patches and is also
independently merged by a couple of other trees.
That shouldn't cause any conflicts by itself.

Saeed Mahameed <saeedm@mellanox.com> says:

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mlx5-next is a very small branch based on a very early rc that includes
mlx5 shared stuff between rdma and net-next, and now virtio as well.

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Signed-off-by: Michael S. Tsirkin <mst@redhat.com>