net: phy: mdio-bcm-unimac: Add BCM6846 support

Add Unimac mdio compatible string for the special BCM6846
variant.

This variant has a few extra registers compared to other
versions.

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>
Link: https://patch.msgid.link/20241012-bcm6846-mdio-v1-2-c703ca83e962@linaro.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: Linus Walleij

drivers/net/mdio/mdio-bcm-unimac.c

@@ -337,6 +337,7 @@ static const struct of_device_id unimac_mdio_ids[] = {
 	{ .compatible = "brcm,asp-v2.2-mdio", },
 	{ .compatible = "brcm,asp-v2.1-mdio", },
 	{ .compatible = "brcm,asp-v2.0-mdio", },
+	{ .compatible = "brcm,bcm6846-mdio", },
 	{ .compatible = "brcm,genet-mdio-v5", },
 	{ .compatible = "brcm,genet-mdio-v4", },
 	{ .compatible = "brcm,genet-mdio-v3", },