net/mlx5: Expose vDPA emulation device capabilities

Expose vDPA emulation device capabilities from the core layer.
It includes reading the capabilities from the firmware and exposing
helper functions to access the data.

Signed-off-by: Yishai Hadas <yishaih@mellanox.com>
Reviewed-by: Shahaf Shuler <shahafs@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>