dt-bindings: net: Add Cortina device tree bindings

Cortina Phy Driver Device Tree Bindings

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CORTINA is a registered trademark of Cortina Systems, Inc.

The driver supports the Cortina Electronic Dispersion Compensation (EDC)

devices, equipped with clock and data recovery (CDR) circuits. These

devices make use of registers that are not compatible with Clause 45 or

Clause 22, therefore they need to be described using the

"ethernet-phy-id" compatible.

Since the driver only implements  polling mode support, interrupts info

can be skipped.

Example (CS4340 phy):

	mdio {

		cs4340_phy@10 {

			compatible = "ethernet-phy-id13e5.1002";

			reg = <0x10>;

		};

	};