dt-bindings: net: document BCM4908 Ethernet controller

BCM4908 is a family of SoCs with integrated Ethernet controller.
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/brcm,bcm4908enet.yaml

+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/net/brcm,bcm4908enet.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Broadcom BCM4908 Ethernet controller
+
+description: Broadcom's Ethernet controller integrated into BCM4908 family SoCs
+
+maintainers:
+  - Rafał Miłecki <rafal@milecki.pl>
+
+properties:
+  compatible:
+    const: brcm,bcm4908enet
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    description: RX interrupt
+
+  interrupt-names:
+    const: rx
+
+required:
+  - reg
+  - interrupts
+  - interrupt-names
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/irq.h>
+    #include <dt-bindings/interrupt-controller/arm-gic.h>
+
+    ethernet@80002000 {
+        compatible = "brcm,bcm4908enet";
+        reg = <0x80002000 0x1000>;
+
+        interrupts = <GIC_SPI 86 IRQ_TYPE_LEVEL_HIGH>;
+        interrupt-names = "rx";
+    };