vdpa/mlx5: introduce Mellanox vDPA driver

vdpa/mlx5: introduce Mellanox vDPA driver

Add a new driver to support vDPA operations by Mellanox devices.

The first Mellanox devices which support vDPA operations are
ConnectX-6 Dx and Bluefield1 HCA for their PF ports and VF ports.

This driver is depending on rdma-core like the mlx5 PMD, also it is
going to use mlx5 DevX to create HW objects directly by the FW.
Hence, the common/mlx5 library is linked to the mlx5_vdpa driver.

This driver will not be compiled by default due to the above
dependencies.

Register a new log type for this driver.

Signed-off-by: Matan Azrad <matan@mellanox.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>