net/mlx5: Introduce and use mlx5_eswitch_get_total_vports()

Instead MLX5_TOTAL_VPORTS, use mlx5_eswitch_get_total_vports().
mlx5_eswitch_get_total_vports() in subsequent patch accounts for SF
vports as well.
Expanding MLX5_TOTAL_VPORTS macro would require exposing SF internals to
more generic vport.h header file. Such exposure is not desired.
Hence a mlx5_eswitch_get_total_vports() is introduced.

Given that mlx5_eswitch_get_total_vports() API wants to work on const
mlx5_core_dev*, change its helper functions also to accept const *dev.

Signed-off-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>