regulator: Add DT bindings for RaspberryPi 7" display ATTINY88-based regulator/backlight controller

Add DT bindings for RaspberryPi 7" display ATTINY88-based
regulator/backlight controller, this one is used in the
Raspberry Pi 7" touchscreen display unit.
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Eric Anholt <eric@anholt.net>
Cc: Mark Brown <broonie@kernel.org>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: devicetree@vger.kernel.org
To: dri-devel@lists.freedesktop.org
Link: https://lore.kernel.org/r/20200809105938.6388-1-marex@denx.deSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/regulator/raspberrypi,7inch-touchscreen-panel-regulator.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/regulator/raspberrypi,7inch-touchscreen-panel-regulator.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: RaspberryPi 7" display ATTINY88-based regulator/backlight controller
+
+maintainers:
+  - Marek Vasut <marex@denx.de>
+
+description: |
+  The RaspberryPi 7" display has an ATTINY88-based regulator/backlight
+  controller on the PCB, which is used to turn the display unit on/off
+  and control the backlight.
+
+allOf:
+  - $ref: "regulator.yaml#"
+
+properties:
+  compatible:
+    const: raspberrypi,7inch-touchscreen-panel-regulator
+
+  reg:
+    maxItems: 1
+
+additionalProperties: false
+
+required:
+  - compatible
+  - reg
+
+examples:
+  - |
+    i2c {
+      #address-cells = <1>;
+      #size-cells = <0>;
+      regulator@45 {
+        compatible = "raspberrypi,7inch-touchscreen-panel-regulator";
+        reg = <0x45>;
+      };
+    };
+
+...