dt-bindings: max3421-udc: add dt bindings for MAX3420 UDC

Add YAML dt bindings for Maxim MAX3420 UDC controller.
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Felipe Balbi <balbi@kernel.org>

Documentation/devicetree/bindings/usb/maxim,max3420-udc.yaml

+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/usb/maxim,max3420-udc.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: MAXIM MAX3420/1 USB Peripheral Controller
+
+maintainers:
+  - Jassi Brar <jaswinder.singh@linaro.org>
+
+description: |
+  The controller provices USB2.0 compliant FullSpeed peripheral
+  implementation over the SPI interface.
+
+  Specifications about the part can be found at:
+    http://datasheets.maximintegrated.com/en/ds/MAX3420E.pdf
+
+properties:
+  compatible:
+    enum:
+      - maxim,max3420-udc
+      - maxim,max3421-udc
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    items:
+      - description: usb irq from max3420
+      - description: vbus detection irq
+    minItems: 1
+    maxItems: 2
+
+  interrupt-names:
+    items:
+      - const: udc
+      - const: vbus
+    minItems: 1
+    maxItems: 2
+
+  spi-max-frequency:
+    maximum: 26000000
+
+required:
+  - compatible
+  - reg
+  - interrupts
+  - interrupt-names
+
+additionalProperties: false
+
+examples:
+  - |
+      #include <dt-bindings/gpio/gpio.h>
+      #include <dt-bindings/interrupt-controller/irq.h>
+      spi0 {
+            #address-cells = <1>;
+            #size-cells = <0>;
+
+            udc@0 {
+                  compatible = "maxim,max3420-udc";
+                  reg = <0>;
+                  interrupt-parent = <&gpio>;
+                  interrupts = <0 IRQ_TYPE_EDGE_FALLING>, <10 IRQ_TYPE_EDGE_BOTH>;
+                  interrupt-names = "udc", "vbus";
+                  spi-max-frequency = <12500000>;
+            };
+      };