dt-bindings: net: ks8851: Convert to YAML schema

Convert the Micrel KSZ8851 DT bindings to YAML schema.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Andrew Lunn <andrew@lunn.ch>
Cc: David S. Miller <davem@davemloft.net>
Cc: Lukas Wunner <lukas@wunner.de>
Cc: Petr Stetiar <ynezz@true.cz>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: linux@dh-electronics.com
Cc: netdev@vger.kernel.org
To: devicetree@vger.kernel.org
Link: https://lore.kernel.org/r/20210620210741.100206-1-marex@denx.de


Signed-off-by: Rob Herring <robh@kernel.org>