dt-bindings: gpio: add NPCM sgpio driver bindings

Add dt-bindings document for the Nuvoton NPCM7xx sgpio driver
Signed-off-by: Jim Liu <JJLIU0@nuvoton.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

Documentation/devicetree/bindings/gpio/nuvoton,sgpio.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/gpio/nuvoton,sgpio.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Nuvoton SGPIO controller
+
+maintainers:
+  - Jim LIU <JJLIU0@nuvoton.com>
+
+description: |
+  This SGPIO controller is for NUVOTON NPCM7xx and NPCM8xx SoC and detailed
+  information is in the NPCM7XX/8XX SERIAL I/O EXPANSION INTERFACE section.
+  Nuvoton NPCM7xx SGPIO module is combines a serial to parallel IC (HC595)
+  and a parallel to serial IC (HC165).
+  Clock is a division of the APB3 clock.
+  This interface has 4 pins (D_out , D_in, S_CLK, LDSH).
+  NPCM7xx/NPCM8xx have two sgpio modules. Each module can support up
+  to 64 output pins, and up to 64 input pins, the pin is only for GPI or GPO.
+  GPIO pins can be programmed to support the following options
+  - Support interrupt option for each input port and various interrupt
+    sensitivity options (level-high, level-low, edge-high, edge-low)
+  - ngpios is number of nuvoton,input-ngpios GPIO lines and nuvoton,output-ngpios GPIO lines.
+    nuvoton,input-ngpios GPIO lines is only for GPI.
+    nuvoton,output-ngpios GPIO lines is only for GPO.
+
+properties:
+  compatible:
+    enum:
+      - nuvoton,npcm750-sgpio
+      - nuvoton,npcm845-sgpio
+
+  reg:
+    maxItems: 1
+
+  gpio-controller: true
+
+  '#gpio-cells':
+    const: 2
+
+  interrupts:
+    maxItems: 1
+
+  clocks:
+    maxItems: 1
+
+  nuvoton,input-ngpios:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description:
+      The numbers of GPIO's exposed. GPIO lines are only for GPI.
+    minimum: 0
+    maximum: 64
+
+  nuvoton,output-ngpios:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description:
+      The numbers of GPIO's exposed. GPIO lines are only for GPO.
+    minimum: 0
+    maximum: 64
+
+required:
+  - compatible
+  - reg
+  - gpio-controller
+  - '#gpio-cells'
+  - interrupts
+  - nuvoton,input-ngpios
+  - nuvoton,output-ngpios
+  - clocks
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/clock/nuvoton,npcm7xx-clock.h>
+    #include <dt-bindings/interrupt-controller/arm-gic.h>
+    gpio8: gpio@101000 {
+        compatible = "nuvoton,npcm750-sgpio";
+        reg = <0x101000 0x200>;
+        clocks = <&clk NPCM7XX_CLK_APB3>;
+        interrupts = <GIC_SPI 19 IRQ_TYPE_LEVEL_HIGH>;
+        gpio-controller;
+        #gpio-cells = <2>;
+        nuvoton,input-ngpios = <64>;
+        nuvoton,output-ngpios = <64>;
+    };