vdpa/mlx5: Make hardware definitions visible to all mlx5 devices

Move mlx5_vdpa IFC header file to the general include folder, so
mlx5_core will be able to reuse it to check if VDPA is supported
prior to creating an auxiliary device.

As part of this move, update the header file name to mlx5 general
naming scheme.

Reviewed-by: Parav Pandit <parav@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>