dt-bindings: net: renesas,rzn1-gmac: Document RZ/N1 GMAC support

The RZ/N1 series of MPUs feature up to two Gigabit Ethernet controllers.
These controllers are based on Synopsys IPs. They can be connected to
RZ/N1 RGMII/RMII converters.

Add a binding that describes these GMAC devices.
Signed-off-by: Clément Léger <clement.leger@bootlin.com>
[rgantois: commit log]
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Romain Gantois <romain.gantois@bootlin.com>
Link: https://lore.kernel.org/r/20240513-rzn1-gmac1-v7-1-6acf58b5440d@bootlin.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/devicetree/bindings/net/renesas,rzn1-gmac.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/net/renesas,rzn1-gmac.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Renesas GMAC
+
+maintainers:
+  - Romain Gantois <romain.gantois@bootlin.com>
+
+select:
+  properties:
+    compatible:
+      contains:
+        enum:
+          - renesas,r9a06g032-gmac
+          - renesas,rzn1-gmac
+  required:
+    - compatible
+
+allOf:
+  - $ref: snps,dwmac.yaml#
+
+properties:
+  compatible:
+    items:
+      - enum:
+          - renesas,r9a06g032-gmac
+      - const: renesas,rzn1-gmac
+      - const: snps,dwmac
+
+  pcs-handle:
+    description:
+      phandle pointing to a PCS sub-node compatible with
+      renesas,rzn1-miic.yaml#
+
+required:
+  - compatible
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/clock/r9a06g032-sysctrl.h>
+    #include <dt-bindings/interrupt-controller/arm-gic.h>
+
+    ethernet@44000000 {
+      compatible = "renesas,r9a06g032-gmac", "renesas,rzn1-gmac", "snps,dwmac";
+      reg = <0x44000000 0x2000>;
+      interrupts = <GIC_SPI 34 IRQ_TYPE_LEVEL_HIGH>,
+                   <GIC_SPI 36 IRQ_TYPE_LEVEL_HIGH>,
+                   <GIC_SPI 35 IRQ_TYPE_LEVEL_HIGH>;
+      interrupt-names = "macirq", "eth_wake_irq", "eth_lpi";
+      clock-names = "stmmaceth";
+      clocks = <&sysctrl R9A06G032_HCLK_GMAC0>;
+      power-domains = <&sysctrl>;
+      snps,multicast-filter-bins = <256>;
+      snps,perfect-filter-entries = <128>;
+      tx-fifo-depth = <2048>;
+      rx-fifo-depth = <4096>;
+      pcs-handle = <&mii_conv1>;
+      phy-mode = "mii";
+    };
+
+...