dt-bindings: net: add a binding document for MediaTek STAR Ethernet MAC

This adds yaml DT bindings for the MediaTek STAR Ethernet MAC present
on the mt8* family of SoCs.
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/mediatek,eth-mac.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/net/mediatek,eth-mac.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: MediaTek STAR Ethernet MAC Controller
+
+maintainers:
+  - Bartosz Golaszewski <bgolaszewski@baylibre.com>
+
+description:
+  This Ethernet MAC is used on the MT8* family of SoCs from MediaTek.
+  It's compliant with 802.3 standards and supports half- and full-duplex
+  modes with flow-control as well as CRC offloading and VLAN tags.
+
+allOf:
+  - $ref: "ethernet-controller.yaml#"
+
+properties:
+  compatible:
+    enum:
+      - mediatek,mt8516-eth
+      - mediatek,mt8518-eth
+      - mediatek,mt8175-eth
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  clocks:
+    minItems: 3
+    maxItems: 3
+
+  clock-names:
+    additionalItems: false
+    items:
+      - const: core
+      - const: reg
+      - const: trans
+
+  mediatek,pericfg:
+    $ref: /schemas/types.yaml#definitions/phandle
+    description:
+      Phandle to the device containing the PERICFG register range. This is used
+      to control the MII mode.
+
+  mdio:
+    type: object
+    description:
+      Creates and registers an MDIO bus.
+
+required:
+  - compatible
+  - reg
+  - interrupts
+  - clocks
+  - clock-names
+  - mediatek,pericfg
+  - phy-handle
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/arm-gic.h>
+    #include <dt-bindings/clock/mt8516-clk.h>
+
+    ethernet: ethernet@11180000 {
+        compatible = "mediatek,mt8516-eth";
+        reg = <0x11180000 0x1000>;
+        mediatek,pericfg = <&pericfg>;
+        interrupts = <GIC_SPI 111 IRQ_TYPE_LEVEL_LOW>;
+        clocks = <&topckgen CLK_TOP_RG_ETH>,
+                 <&topckgen CLK_TOP_66M_ETH>,
+                 <&topckgen CLK_TOP_133M_ETH>;
+        clock-names = "core", "reg", "trans";
+        phy-handle = <&eth_phy>;
+        phy-mode = "rmii";
+
+        mdio {
+            #address-cells = <1>;
+            #size-cells = <0>;
+
+            eth_phy: ethernet-phy@0 {
+                reg = <0>;
+            };
+        };
+    };