dt-bindings: net: dsa: lantiq,gswip: add MaxLinear RMII refclk output property

dt-bindings: net: dsa: lantiq,gswip: add MaxLinear RMII refclk output property

Add support for the maxlinear,rmii-refclk-out boolean property on port
nodes to configure the RMII reference clock to be an output rather than
an input.

This property is only applicable for ports in RMII mode and allows the
switch to provide the reference clock for RMII-connected PHYs instead
of requiring an external clock source.

This corresponds to the driver changes that read this Device Tree
property to configure the RMII clock direction.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Reviewed-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://patch.msgid.link/9813bb916ecce9bae366e6c50c081014fe5371ea.1762170107.git.daniel@makrotopia.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>