vdpa/mlx5: Support configuring max data virtqueue

Check whether the max number of data virtqueue pairs was provided when a
adding a new device and verify the new value does not exceed device
capabilities.

In addition, change the arrays holding virtqueue and callback contexts
to be dynamically allocated.

Signed-off-by: Eli Cohen <elic@nvidia.com>
Link: https://lore.kernel.org/r/20220105114646.577224-8-elic@nvidia.com

Includes fixup:

vdpa/mlx5: fix error handling in mlx5_vdpa_dev_add()

Clang build fails with
mlx5_vnet.c:2574:6: error: variable 'mvdev' is used uninitialized whenever
  'if' condition is true
        if (!ndev->vqs || !ndev->event_cbs) {
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
mlx5_vnet.c:2660:14: note: uninitialized use occurs here
        put_device(&mvdev->vdev.dev);
                    ^~~~~
This because mvdev is set after trying to allocate ndev->vqs,event_cbs.
So move the allocation to after mvdev is set but before the arrays
are used in init_mvqs()

Signed-off-by: Tom Rix <trix@redhat.com>
Link: https://lore.kernel.org/r/20220107211352.3940570-1-trix@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

Includes fixup:

vdpa/mlx5: fix endian-ness for max vqs

sparse warnings: (new ones prefixed by >>)
>> drivers/vdpa/mlx5/net/mlx5_vnet.c:1247:23: sparse: sparse: cast to restricted __le16
>> drivers/vdpa/mlx5/net/mlx5_vnet.c:1247:23: sparse: sparse: cast from restricted __virtio16

> 1247                  num = le16_to_cpu(ndev->config.max_virtqueue_pairs);

Address this using the appropriate wrapper.

Cc: "Eli Cohen" <elic@nvidia.com>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Eli Cohen <elic@nvidia.com>