net/mlx5: E-Switch, Use getter and iterator to access vport/rep

With only PF and VF, it is sufficient to have the vport/rep array
index as the vport number. This is because PF and VF vports numbers
are consecutive serial numbers. In downstream patches with
introducing of ECPF and UPLINK vports, it's not consecutive any more.

Use getter to get specific vport/rep, and use iterator to traversal
a list of vport/rep. This hides the translation between array index
and vport number, and provides flexibility of using different
translation mechanism in the future.

This patch doesn't change any functionality.

Signed-off-by: Bodong Wang <bodong@mellanox.com>
Suggested-by: Saeed Mahameed <saeedm@mellanox.com>
Reviewed-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>