net/mlx5_core: Make the vport helpers available for the IB driver too

Move the vport header file to be under include/linux/mlx5, such that
the mlx5 IB can use it as well.

Also add nic_ prefix to the vport NIC commands to differeniate between
HCA vport commands and NIC vport commands.

Signed-off-by: Majd Dibbiny <majd@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>