net: dsa: mt7530: put initialising PCS devices code back to original order

The commit fae46308 ("net: dsa: mt753x: fix pcs conversion regression")
fixes regression caused by cpu_port_config manually calling phylink
operations. cpu_port_config was deemed useless and was removed. Therefore,
put initialising PCS devices code back to its original order.

Signed-off-by: Arınç ÜNAL <arinc.unal@arinc9.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>