dt-bindings: net: mdio-gpio: add compatible for microchip,mdio-smi0

dt-bindings: net: mdio-gpio: add compatible for microchip,mdio-smi0

Microchip SMI0 Mode is a special mode, where the MDIO Read/Write
commands are part of the PHY Address and the OP Code is always 0. We add
the compatible for this special mode of the bitbanged mdio driver.

Cc: devicetree@vger.kernel.org
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>