dt-bindings: soc: hisilicon: document hi3660-usb3-otg-bc

Add dedicated bindings for the Hisilicon Kirin 960 USB OTG Syscon,
to fully document the block and also fix dtbs_check warning:

hi3660-hikey960.dtb: usb3_otg_bc@ff200000: compatible: ['syscon', 'simple-mfd'] is too short

Reviewed-by: Conor Dooley <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Krzysztof Kozlowski <[e-mail]>

Documentation/devicetree/bindings/soc/hisilicon/hisilicon,hi3660-usb3-otg-bc.yaml

···
+# SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/soc/hisilicon/hisilicon,hi3660-usb3-otg-bc.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Hisilicon Kirin 960 USB OTG Battery Charging Syscon
+
+maintainers:
+  - Mauro Carvalho Chehab <[e-mail]>
+
+properties:
+  compatible:
+    items:
+      - const: hisilicon,hi3660-usb3-otg-bc
+      - const: syscon
+      - const: simple-mfd
+
+  reg:
+    maxItems: 1
+
+  usb-phy:
+    $ref: /schemas/phy/hisilicon,hi3660-usb3.yaml
+    description: USB Phy node
+
+required:
+  - compatible
+  - reg
+  - usb-phy
+
+additionalProperties: false
+
+examples:
+  - |
+    syscon@ff200000 {
+        compatible = "hisilicon,hi3660-usb3-otg-bc", "syscon", "simple-mfd";
+        reg = <0xff200000 0x1000>;
+
+        usb-phy {
+            compatible = "hisilicon,hi3660-usb-phy";
+            #phy-cells = <0>;
+            hisilicon,pericrg-syscon = <&crg_ctrl>;
+            hisilicon,pctrl-syscon = <&pctrl>;
+            hisilicon,eye-diagram-param = <0x22466e4>;
+        };
+    };