dt-bindings: net: brcm,unimac-mdio: Add bcm6846-mdio

The MDIO block in the BCM6846 is not identical to any of the
previous versions, but has extended registers not present in
the other variants. For this reason we need to use a new
compatible especially for this SoC.

Suggested-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://lore.kernel.org/linux-devicetree/b542b2e8-115c-4234-a464-e73aa6bece5c@broadcom.com/


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20241012-bcm6846-mdio-v1-1-c703ca83e962@linaro.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>