net: dsa: b53: allow RGMII for bcm63xx RGMII ports

Add RGMII to supported interfaces for BCM63xx RGMII ports so they can be
actually used in RGMII mode.

Without this, phylink will fail to configure them:

[    3.580000] b53-switch 10700000.switch GbE3 (uninitialized): validation of rgmii with support 0000000,00000000,00000000,000062ff and advertisement 0000000,00000000,00000000,000062ff failed: -EINVAL
[    3.600000] b53-switch 10700000.switch GbE3 (uninitialized): failed to connect to PHY: -EINVAL
[    3.610000] b53-switch 10700000.switch GbE3 (uninitialized): error -22 setting up PHY for tree 0, switch 0, port 4

Fixes: ce3bf948 ("net: dsa: b53: add support for BCM63xx RGMIIs")
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
Link: https://patch.msgid.link/20250602193953.1010487-5-jonas.gorski@gmail.com


Signed-off-by: Paolo Abeni <pabeni@redhat.com>