Revert "net: dsa: Add more convenient functions for installing port VLANs"

This reverts commit 314f76d7

.

Citing that commit message, the call graph was:

    dsa_slave_vlan_rx_add_vid   dsa_port_setup_8021q_tagging
                |                        |
                |                        |
                |          +-------------+
                |          |
                v          v
               dsa_port_vid_add      dsa_slave_port_obj_add
                      |                         |
                      +-------+         +-------+
                              |         |
                              v         v
                           dsa_port_vlan_add

Now that tag_8021q has its own ops structure, it no longer relies on
dsa_port_vid_add, and therefore on the dsa_switch_ops to install its
VLANs.

So dsa_port_vid_add now only has one single caller. So we can simplify
the call graph to what it was before, aka:

        dsa_slave_vlan_rx_add_vid     dsa_slave_port_obj_add
                      |                         |
                      +-------+         +-------+
                              |         |
                              v         v
                           dsa_port_vlan_add

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>