net: dsa: use ports list to setup switches

Use the new ports list instead of iterating over switches and their
ports when setting up the switches and their ports.

At the same time, provide setup states and messages for ports and
switches as it is done for the trees.

Signed-off-by: Vivien Didelot <vivien.didelot@gmail.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>