dt-bindings: net: dsa: microchip: add mdio-parent-bus property for internal MDIO

dt-bindings: net: dsa: microchip: add mdio-parent-bus property for internal MDIO

Introduce `mdio-parent-bus` property in the ksz DSA bindings to
reference the parent MDIO bus when the internal MDIO bus is attached to
it, bypassing the main management interface.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20241106075942.1636998-3-o.rempel@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>