net: dsa: b53: do not enable EEE on bcm63xx

net: dsa: b53: do not enable EEE on bcm63xx

BCM63xx internal switches do not support EEE, but provide multiple RGMII
ports where external PHYs may be connected. If one of these PHYs are EEE
capable, we may try to enable EEE for the MACs, which then hangs the
system on access of the (non-existent) EEE registers.

Fix this by checking if the switch actually supports EEE before
attempting to configure it.

Fixes: 22256b0afb12 ("net: dsa: b53: Move EEE functions to b53")
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Tested-by: Álvaro Fernández Rojas <noltari@gmail.com>
Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
Link: https://patch.msgid.link/20250602193953.1010487-2-jonas.gorski@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>