dt-bindings: Add Broadcom STB USB support

Add DT bindings for Broadcom STB USB EHCI and XHCI drivers.

NOTE: The OHCI driver is not included because it uses the generic
      platform driver.
Signed-off-by: Al Cooper <alcooperx@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20200512150019.25903-3-alcooperx@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/usb/brcm,bcm7445-ehci.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/usb/brcm,bcm7445-ehci.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Broadcom STB USB EHCI Controller Device Tree Bindings
+
+allOf:
+  - $ref: "usb-hcd.yaml"
+
+maintainers:
+  - Al Cooper <alcooperx@gmail.com>
+
+properties:
+  compatible:
+    const: brcm,bcm7445-ehci
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  clocks:
+    maxItems: 1
+    description: Clock specifier for the EHCI clock
+
+  clock-names:
+    const: sw_usb
+
+  phys:
+    maxItems: 1
+
+  phy-names:
+    const: usbphy
+
+required:
+  - compatible
+  - reg
+  - interrupts
+  - phys
+  - clocks
+
+additionalProperties: false
+
+examples:
+  - |
+    usb@f0b00300 {
+        compatible = "brcm,bcm7445-ehci";
+        reg = <0xf0b00300 0xa8>;
+        interrupts = <0x0 0x5a 0x0>;
+        phys = <&usbphy_0 0x0>;
+        phy-names = "usbphy";
+        clocks = <&usb20>;
+        clock-names = "sw_usb";
+    };
+
+...

Documentation/devicetree/bindings/usb/usb-xhci.txt

@@ -24,6 +24,7 @@ Required properties:
       device
     - "renesas,rcar-gen3-xhci" for a generic R-Car Gen3 or RZ/G2 compatible
       device
+    - "brcm,bcm7445-xhci" for Broadcom STB SoCs with XHCI
     - "xhci-platform" (deprecated)
 
     When compatible with the generic version, nodes must list the