Merge branch 'net-dsa-b53-clean-up-cpu-imp-ports'

Rafał Miłecki says:

====================
net: dsa: b53: Clean up CPU/IMP ports

This has been tested on:

1. Luxul XBR-4500 with used CPU port 5
[    8.361438] b53-srab-switch 18007000.ethernet-switch: found switch: BCM53012, rev 0

2. Netgear R8000 with used CPU port 8
[    4.453858] b53-srab-switch 18007000.ethernet-switch: found switch: BCM53012, rev 5

====================

Link: https://lore.kernel.org/r/20210916120354.20338-1-zajec5@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>